scala.collection.MapLike

trait MapLike[A, +B, +This <: MapLike[A, B, This] with Map[A, B]] extends PartialFunction[A, B] with IterableLike[(A, B), This] with GenMapLike[A, B, This] with Subtractable[A, This] with Parallelizable[(A, B), ParMap[A, B]]

A template trait for maps, which associate keys with values.

Implementation note: This trait provides most of the operations of a Map independently of its representation. It is typically inherited by concrete implementations of maps.

To implement a concrete map, you need to provide implementations of the following methods:

def get(key: A): Option[B]
def iterator: Iterator[(A, B)]
def + [B1 >: B](kv: (A, B1)): This
def -(key: A): This

If you wish that methods like take , drop , filter also return the same kind of map you should also override:

def empty: This

It is also good idea to override methods foreach and size for efficiency.

• Self Type
  • MapLike [A, B, This]
• Source
  • MapLike.scala - Blame
  • MapLike.scala - History
• Since
  • 2.8

Type Members

class DefaultKeySet extends AbstractSet[A] with Set[A] with Serializable

The implementation class of the set returned by keySet .

• Attributes
  • protected
• Source
  • MapLike.scala - Blame
  • MapLike.scala - History

class DefaultValuesIterable extends AbstractIterable[B] with Iterable[B] with Serializable

The implementation class of the iterable returned by values .

• Attributes
  • protected
• Source
  • MapLike.scala - Blame
  • MapLike.scala - History

class FilteredKeys extends AbstractMap[A, B] with DefaultMap[A, B]

• Attributes
  • protected
• Source
  • MapLike.scala - Blame
  • MapLike.scala - History

class MappedValues[C] extends AbstractMap[A, C] with DefaultMap[A, C]

• Attributes
  • protected
• Source
  • MapLike.scala - Blame
  • MapLike.scala - History

type Self = This

The type implementing this traversable

• Attributes
  • protected[this]
• Definition Classes
  • TraversableLike

class WithFilter extends FilterMonadic[A, Repr]

A class supporting filtered operations. Instances of this class are returned by method withFilter .

• Definition Classes
  • TraversableLike

Concrete Value Members From scala.Function1

def compose[A](g: (A) ⇒ A): (A) ⇒ B

Composes two instances of Function1 in a new Function1, with this function applied last.

• A
  • the type to which function g can be applied
• g
  • a function A => T1
• returns
  • a new function f such that f(x) == apply(g(x))
• Definition Classes
  • Function1
• Annotations
  • @ unspecialized ()

(defined at scala.Function1)

Concrete Value Members From scala.PartialFunction

def andThen[C](k: (B) ⇒ C): PartialFunction[A, C]

Composes this partial function with a transformation function that gets applied to results of this partial function.

• C
  • the result type of the transformation function.
• k
  • the transformation function
• returns
  • a partial function with the same domain as this partial function, which maps arguments x to k(this(x)) .
• Definition Classes
  • PartialFunction → Function1

(defined at scala.PartialFunction)

def applyOrElse[A1 <: A, B1 >: B](x: A1, default: (A1) ⇒ B1): B1

Applies this partial function to the given argument when it is contained in the function domain. Applies fallback function where this partial function is not defined.

Note that expression pf.applyOrElse(x, default) is equivalent to

if(pf isDefinedAt x) pf(x) else default(x)

except that applyOrElse method can be implemented more efficiently. For all partial function literals the compiler generates an applyOrElse implementation which avoids double evaluation of pattern matchers and guards. This makes applyOrElse the basis for the efficient implementation for many operations and scenarios, such as:

• combining partial functions into orElse / andThen chains does not lead to excessive apply / isDefinedAt evaluation
• lift and unlift do not evaluate source functions twice on each invocation
• runWith allows efficient imperative-style combining of partial functions with conditionally applied actions

For non-literal partial function classes with nontrivial isDefinedAt method it is recommended to override applyOrElse with custom implementation that avoids double isDefinedAt evaluation. This may result in better performance and more predictable behavior w.r.t. side effects.

• x
  • the function argument
• default
  • the fallback function
• returns
  • the result of this function or fallback function application.
• Definition Classes
  • PartialFunction
• Since
  • 2.10

(defined at scala.PartialFunction)

def lift: (A) ⇒ Option[B]

Turns this partial function into a plain function returning an Option result.

• returns
  • a function that takes an argument x to Some(this(x)) if this is defined for x , and to None otherwise.
• Definition Classes
  • PartialFunction
• See also
  • Function.unlift

(defined at scala.PartialFunction)

def orElse[A1 <: A, B1 >: B](that: PartialFunction[A1, B1]): PartialFunction[A1, B1]

Composes this partial function with a fallback partial function which gets applied where this partial function is not defined.

• A1
  • the argument type of the fallback function
• B1
  • the result type of the fallback function
• that
  • the fallback function
• returns
  • a partial function which has as domain the union of the domains of this partial function and that . The resulting partial function takes x to this(x) where this is defined, and to that(x) where it is not.
• Definition Classes
  • PartialFunction

(defined at scala.PartialFunction)

def runWith[U](action: (B) ⇒ U): (A) ⇒ Boolean

Composes this partial function with an action function which gets applied to results of this partial function. The action function is invoked only for its side effects; its result is ignored.

Note that expression pf.runWith(action)(x) is equivalent to

if(pf isDefinedAt x) { action(pf(x)); true } else false

except that runWith is implemented via applyOrElse and thus potentially more efficient. Using runWith avoids double evaluation of pattern matchers and guards for partial function literals.

• action
  • the action function
• returns
  • a function which maps arguments x to isDefinedAt(x) . The resulting function runs action(this(x)) where this is defined.
• Definition Classes
  • PartialFunction
• Since
  • 2.10
• See also
  • applyOrElse .

(defined at scala.PartialFunction)

Abstract Value Members From scala.collection.GenMapLike

abstract def seq: Map[A, B]

• Definition Classes
  • GenMapLike → Parallelizable → GenTraversableOnce

(defined at scala.collection.GenMapLike)

Concrete Value Members From scala.collection.GenMapLike

def equals(that: Any): Boolean

Compares two maps structurally; i.e., checks if all mappings contained in this map are also contained in the other map, and vice versa.

• that
  • the other map
• returns
  • true if both maps contain exactly the same mappings, false otherwise.
• Definition Classes
  • GenMapLike → Equals → AnyRef → Any

(defined at scala.collection.GenMapLike)

Concrete Value Members From scala.collection.IterableLike

def canEqual(that: Any): Boolean

Method called from equality methods, so that user-defined subclasses can refuse to be equal to other collections of the same kind.

• that
  • The object with which this iterable collection should be compared
• returns
  • true , if this iterable collection can possibly equal that , false otherwise. The test takes into consideration only the run-time types of objects but ignores their elements.
• Definition Classes
  • IterableLike → Equals

(defined at scala.collection.IterableLike)

def copyToArray[B >: (A, B)](xs: Array[B], start: Int, len: Int): Unit

[use case]

Copies the elements of this map to an array. Fills the given array xs with at most len elements of this map, starting at position start . Copying will stop once either the end of the current map is reached, or the end of the target array is reached, or len elements have been copied.

• xs
  • the array to fill.
• start
  • the starting index.
• len
  • the maximal number of elements to copy.
• Definition Classes
  • IterableLike → TraversableLike → TraversableOnce → GenTraversableOnce

(defined at scala.collection.IterableLike)

def drop(n: Int): This

Selects all elements except first n ones.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• n
  • the number of elements to drop from this iterable collection.
• returns
  • a iterable collection consisting of all elements of this iterable collection except the first n ones, or else the empty iterable collection, if this iterable collection has less than n elements.
• Definition Classes
  • IterableLike → TraversableLike → GenTraversableLike

(defined at scala.collection.IterableLike)

def dropRight(n: Int): This

Selects all elements except last n ones.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• n
  • The number of elements to take
• returns
  • a iterable collection consisting of all elements of this iterable collection except the last n ones, or else the empty iterable collection, if this iterable collection has less than n elements.
• Definition Classes
  • IterableLike

(defined at scala.collection.IterableLike)

def exists(p: ((A, B)) ⇒ Boolean): Boolean

Tests whether a predicate holds for at least one element of this iterable collection.

Note: may not terminate for infinite-sized collections.

• p
  • the predicate used to test elements.
• returns
  • false if this iterable collection is empty, otherwise true if the given predicate p holds for some of the elements of this iterable collection, otherwise false
• Definition Classes
  • IterableLike → TraversableLike → TraversableOnce → GenTraversableOnce

(defined at scala.collection.IterableLike)

def find(p: ((A, B)) ⇒ Boolean): Option[(A, B)]

Finds the first element of the iterable collection satisfying a predicate, if any.

Note: may not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• p
  • the predicate used to test elements.
• returns
  • an option value containing the first element in the iterable collection that satisfies p , or None if none exists.
• Definition Classes
  • IterableLike → TraversableLike → TraversableOnce → GenTraversableOnce

(defined at scala.collection.IterableLike)

def foldRight[B](z: B)(op: ((A, B), B) ⇒ B): B

Applies a binary operator to all elements of this iterable collection and a start value, going right to left.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered. or the operator is associative and commutative.

• B
  • the result type of the binary operator.
• z
  • the start value.
• op
  • the binary operator.
• returns
  • the result of inserting op between consecutive elements of this iterable collection, going right to left with the start value z on the right:

    op(x_1, op(x_2, ... op(x_n, z)...))
    

where `x1, ..., xn` are the elements of this iterable collection. Returns
 `z` if this iterable collection is empty.

• Definition Classes
  • IterableLike → TraversableOnce → GenTraversableOnce

(defined at scala.collection.IterableLike)

def forall(p: ((A, B)) ⇒ Boolean): Boolean

Tests whether a predicate holds for all elements of this iterable collection.

Note: may not terminate for infinite-sized collections.

• p
  • the predicate used to test elements.
• returns
  • true if this iterable collection is empty or the given predicate p holds for all elements of this iterable collection, otherwise false .
• Definition Classes
  • IterableLike → TraversableLike → TraversableOnce → GenTraversableOnce

(defined at scala.collection.IterableLike)

def foreach[U](f: ((A, B)) ⇒ U): Unit

[use case]

Applies a function f to all elements of this map.

Note: this method underlies the implementation of most other bulk operations. Subclasses should re-implement this method if a more efficient implementation exists.

• f
  • the function that is applied for its side-effect to every element. The result of function f is discarded.
• Definition Classes
  • IterableLike → TraversableLike → GenTraversableLike → TraversableOnce → GenTraversableOnce → FilterMonadic

(defined at scala.collection.IterableLike)

def grouped(size: Int): Iterator[This]

Partitions elements in fixed size iterable collections.

• size
  • the number of elements per group
• returns
  • An iterator producing iterable collections of size size , except the last will be less than size size if the elements don’t divide evenly.
• Definition Classes
  • IterableLike
• See also
  • scala.collection.Iterator, method grouped

(defined at scala.collection.IterableLike)

def head: (A, B)

Selects the first element of this iterable collection.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• returns
  • the first element of this iterable collection.
• Definition Classes
  • IterableLike → TraversableLike → GenTraversableLike
• Exceptions thrown
  • NoSuchElementException if the iterable collection is empty.

(defined at scala.collection.IterableLike)

def reduceRight[B >: (A, B)](op: ((A, B), B) ⇒ B): B

Applies a binary operator to all elements of this iterable collection, going right to left.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered. or the operator is associative and commutative.

• B
  • the result type of the binary operator.
• op
  • the binary operator.
• returns
  • the result of inserting op between consecutive elements of this iterable collection, going right to left:

    op(x_1, op(x_2, ..., op(x_{n-1}, x_n)...))
    

where `x1, ..., xn` are the elements of this iterable collection.

• Definition Classes
  • IterableLike → TraversableOnce → GenTraversableOnce
• Exceptions thrown
  • UnsupportedOperationException if this iterable collection is empty.

(defined at scala.collection.IterableLike)

def sameElements[B >: (A, B)](that: GenIterable[B]): Boolean

[use case]

Checks if the other iterable collection contains the same elements in the same order as this map.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• that
  • the collection to compare with.
• returns
  • true , if both collections contain the same elements in the same order, false otherwise.
• Definition Classes
  • IterableLike → GenIterableLike

(defined at scala.collection.IterableLike)

def slice(from: Int, until: Int): This

Selects an interval of elements. The returned collection is made up of all elements x which satisfy the invariant:

from <= indexOf(x) < until

Note: might return different results for different runs, unless the underlying collection type is ordered.

• returns
  • a iterable collection containing the elements greater than or equal to index from extending up to (but not including) index until of this iterable collection.
• Definition Classes
  • IterableLike → TraversableLike → GenTraversableLike

(defined at scala.collection.IterableLike)

def sliding(size: Int): Iterator[This]

Groups elements in fixed size blocks by passing a “sliding window” over them (as opposed to partitioning them, as is done in grouped.) “Sliding window” step is 1 by default.

• size
  • the number of elements per group
• returns
  • An iterator producing iterable collections of size size , except the last and the only element will be truncated if there are fewer elements than size.
• Definition Classes
  • IterableLike
• See also
  • scala.collection.Iterator, method sliding

(defined at scala.collection.IterableLike)

def sliding(size: Int, step: Int): Iterator[This]

Groups elements in fixed size blocks by passing a “sliding window” over them (as opposed to partitioning them, as is done in grouped.)

• size
  • the number of elements per group
• step
  • the distance between the first elements of successive groups
• returns
  • An iterator producing iterable collections of size size , except the last and the only element will be truncated if there are fewer elements than size.
• Definition Classes
  • IterableLike
• See also
  • scala.collection.Iterator, method sliding

(defined at scala.collection.IterableLike)

def take(n: Int): This

Selects first n elements.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• n
  • the number of elements to take from this iterable collection.
• returns
  • a iterable collection consisting only of the first n elements of this iterable collection, or else the whole iterable collection, if it has less than n elements.
• Definition Classes
  • IterableLike → TraversableLike → GenTraversableLike

(defined at scala.collection.IterableLike)

def takeRight(n: Int): This

Selects last n elements.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• n
  • the number of elements to take
• returns
  • a iterable collection consisting only of the last n elements of this iterable collection, or else the whole iterable collection, if it has less than n elements.
• Definition Classes
  • IterableLike

(defined at scala.collection.IterableLike)

def takeWhile(p: ((A, B)) ⇒ Boolean): This

Takes longest prefix of elements that satisfy a predicate.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• returns
  • the longest prefix of this iterable collection whose elements all satisfy the predicate p .
• Definition Classes
  • IterableLike → TraversableLike → GenTraversableLike

(defined at scala.collection.IterableLike)

def thisCollection: Iterable[(A, B)]

The underlying collection seen as an instance of Iterable . By default this is implemented as the current collection object itself, but this can be overridden.

• Attributes
  • protected[this]
• Definition Classes
  • IterableLike → TraversableLike

(defined at scala.collection.IterableLike)

def toCollection(repr: This): Iterable[(A, B)]

A conversion from collections of type Repr to Iterable objects. By default this is implemented as just a cast, but this can be overridden.

• Attributes
  • protected[this]
• Definition Classes
  • IterableLike → TraversableLike

(defined at scala.collection.IterableLike)

def toIterable: Iterable[(A, B)]

Returns this iterable collection as an iterable collection.

A new collection will not be built; lazy collections will stay lazy.

Note: will not terminate for infinite-sized collections.

• returns
  • an Iterable containing all elements of this iterable collection.
• Definition Classes
  • IterableLike → TraversableOnce → GenTraversableOnce

(defined at scala.collection.IterableLike)

def toIterator: Iterator[(A, B)]

Returns an Iterator over the elements in this iterable collection. Produces the same result as iterator .

Note: will not terminate for infinite-sized collections.

• returns
  • an Iterator containing all elements of this iterable collection.
• Definition Classes
  • IterableLike → TraversableLike → GenTraversableOnce
• Annotations
  • @ deprecatedOverriding (message =…, since = “2.11.0”)

(defined at scala.collection.IterableLike)

def toStream: immutable.Stream[(A, B)]

Converts this iterable collection to a stream.

• returns
  • a stream containing all elements of this iterable collection.
• Definition Classes
  • IterableLike → TraversableLike → GenTraversableOnce

(defined at scala.collection.IterableLike)

def view(from: Int, until: Int): IterableView[(A, B), This]

Creates a non-strict view of a slice of this iterable collection.

Note: the difference between view and slice is that view produces a view of the current iterable collection, whereas slice produces a new iterable collection.

Note: view(from, to) is equivalent to view.slice(from, to)

Note: might return different results for different runs, unless the underlying collection type is ordered.

• from
  • the index of the first element of the view
• until
  • the index of the element following the view
• returns
  • a non-strict view of a slice of this iterable collection, starting at index from and extending up to (but not including) index until .
• Definition Classes
  • IterableLike → TraversableLike

(defined at scala.collection.IterableLike)

def view: IterableView[(A, B), This]

Creates a non-strict view of this iterable collection.

• returns
  • a non-strict view of this iterable collection.
• Definition Classes
  • IterableLike → TraversableLike

(defined at scala.collection.IterableLike)

def zipAll[B, A1 >: (A, B), That](that: GenIterable[B], thisElem: A1, thatElem: B)(implicit bf: CanBuildFrom[This, (A1, B), That]): That

[use case]

Returns a map formed from this map and another iterable collection by combining corresponding elements in pairs. If one of the two collections is shorter than the other, placeholder elements are used to extend the shorter collection to the length of the longer.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• B
  • the type of the second half of the returned pairs
• that
  • The iterable providing the second half of each result pair
• thisElem
  • the element to be used to fill up the result if this map is shorter than that .
• thatElem
  • the element to be used to fill up the result if that is shorter than this map.
• returns
  • a new map containing pairs consisting of corresponding elements of this map and that . The length of the returned collection is the maximum of the lengths of this map and that . If this map is shorter than that , thisElem values are used to pad the result. If that is shorter than this map, thatElem values are used to pad the result.
• Definition Classes
  • IterableLike → GenIterableLike

(defined at scala.collection.IterableLike)

def zipWithIndex[A1 >: (A, B), That](implicit bf: CanBuildFrom[This, (A1, Int), That]): That

[use case]

Zips this map with its indices.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• returns
  • A new map containing pairs consisting of all elements of this map paired with their index. Indices start at 0 .
• Definition Classes
  • IterableLike → GenIterableLike

Example:

List("a", "b", "c").zipWithIndex = List(("a", 0), ("b", 1), ("c", 2))

(defined at scala.collection.IterableLike)

def zip[A1 >: (A, B), B, That](that: GenIterable[B])(implicit bf: CanBuildFrom[This, (A1, B), That]): That

[use case]

Returns a map formed from this map and another iterable collection by combining corresponding elements in pairs. If one of the two collections is longer than the other, its remaining elements are ignored.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• B
  • the type of the second half of the returned pairs
• that
  • The iterable providing the second half of each result pair
• returns
  • a new map containing pairs consisting of corresponding elements of this map and that . The length of the returned collection is the minimum of the lengths of this map and that .
• Definition Classes
  • IterableLike → GenIterableLike

(defined at scala.collection.IterableLike)

Abstract Value Members From scala.collection.MapLike

abstract def get(key: A): Option[B]

Optionally returns the value associated with a key.

• key
  • the key value
• returns
  • an option value containing the value associated with key in this map, or None if none exists.
• Definition Classes
  • MapLike → GenMapLike

(defined at scala.collection.MapLike)

Concrete Value Members From scala.collection.MapLike

abstract def empty: This

The empty map of the same type as this map

• returns
  • an empty map of type This .

(defined at scala.collection.MapLike)

abstract def +[B1 >: B](kv: (A, B1)): Map[A, B1]

[use case]

Adds a key/value pair to this map, returning a new map.

• kv
  • the key/value pair
• returns
  • a new map with the new binding added to this map
• Definition Classes
  • MapLike → GenMapLike

(defined at scala.collection.MapLike)

def +[B1 >: B](kv1: (A, B1), kv2: (A, B1), kvs: (A, B1)*): Map[A, B1]

[use case]

Adds key/value pairs to this map, returning a new map.

This method takes two or more key/value pairs. Another overloaded variant of this method handles the case where a single key/value pair is added.

• kvs
  • the key/value pairs
• returns
  • a new map with the given bindings added to this map

(defined at scala.collection.MapLike)

def ++[B1 >: B](xs: GenTraversableOnce[(A, B1)]): Map[A, B1]

[use case]

Adds all key/value pairs in a traversable collection to this map, returning a new map.

• xs
  • the collection containing the added key/value pairs
• returns
  • a new map with the given bindings added to this map

(defined at scala.collection.MapLike)

abstract def -(key: A): This

[use case]

Removes a key from this map, returning a new map.

• key
  • the key to be removed
• returns
  • a new map without a binding for key
• Definition Classes
  • MapLike → Subtractable → GenMapLike

(defined at scala.collection.MapLike)

def addString(b: StringBuilder, start: String, sep: String, end: String): StringBuilder

Appends all bindings of this map to a string builder using start, end, and separator strings. The written text begins with the string start and ends with the string end . Inside, the string representations of all bindings of this map in the form of key -> value are separated by the string sep .

• b
  • the builder to which strings are appended.
• start
  • the starting string.
• sep
  • the separator string.
• end
  • the ending string.
• returns
  • the string builder b to which elements were appended.
• Definition Classes
  • MapLike → TraversableOnce

(defined at scala.collection.MapLike)

def apply(key: A): B

Retrieves the value which is associated with the given key. This method invokes the default method of the map if there is no mapping from the given key to a value. Unless overridden, the default method throws a NoSuchElementException .

• key
  • the key
• returns
  • the value associated with the given key, or the result of the map’s default method, if none exists.
• Definition Classes
  • MapLike → GenMapLike → Function1

(defined at scala.collection.MapLike)

def contains(key: A): Boolean

Tests whether this map contains a binding for a key.

• key
  • the key
• returns
  • true if there is a binding for key in this map, false otherwise.
• Definition Classes
  • MapLike → GenMapLike

(defined at scala.collection.MapLike)

def default(key: A): B

Defines the default value computation for the map, returned when a key is not found The method implemented here throws an exception, but it might be overridden in subclasses.

• key
  • the given key value for which a binding is missing.
• Definition Classes
  • MapLike → GenMapLike
• Exceptions thrown *

(defined at scala.collection.MapLike)

def filterKeys(p: (A) ⇒ Boolean): Map[A, B]

Filters this map by retaining only keys satisfying a predicate.

Note : the predicate must accept any key of type A , not just those already present in the map, as the predicate is tested before the underlying map is queried.

• p
  • the predicate used to test keys
• returns
  • an immutable map consisting only of those key value pairs of this map where the key satisfies the predicate p . The resulting map wraps the original map without copying any elements.
• Definition Classes
  • MapLike → GenMapLike

(defined at scala.collection.MapLike)

def filterNot(p: ((A, B)) ⇒ Boolean): This

Returns a new map obtained by removing all key/value pairs for which the predicate p returns true .

Note: This method works by successively removing elements for which the predicate is true from this set. If removal is slow, or you expect that most elements of the set will be removed, you might consider using filter with a negated predicate instead.

• p
  • A predicate over key-value pairs
• returns
  • A new map containing elements not satisfying the predicate.
• Definition Classes
  • MapLike → TraversableLike → GenTraversableLike

(defined at scala.collection.MapLike)

def getOrElse[B1 >: B](key: A, default: ⇒ B1): B1

[use case]

Returns the value associated with a key, or a default value if the key is not contained in the map.

• key
  • the key.
• default
  • a computation that yields a default value in case no binding for key is found in the map.
• returns
  • the value associated with key if it exists, otherwise the result of the default computation.
• Definition Classes
  • MapLike → GenMapLike

(defined at scala.collection.MapLike)

def isDefinedAt(key: A): Boolean

Tests whether this map contains a binding for a key. This method, which implements an abstract method of trait PartialFunction , is equivalent to contains .

• key
  • the key
• returns
  • true if there is a binding for key in this map, false otherwise.
• Definition Classes
  • MapLike → GenMapLike → PartialFunction

(defined at scala.collection.MapLike)

def keySet: Set[A]

Collects all keys of this map in a set.

• returns
  • a set containing all keys of this map.
• Definition Classes
  • MapLike → GenMapLike

(defined at scala.collection.MapLike)

def mapValues[C](f: (B) ⇒ C): Map[A, C]

Transforms this map by applying a function to every retrieved value.

• f
  • the function used to transform values of this map.
• returns
  • a map view which maps every key of this map to f(this(key)) . The resulting map wraps the original map without copying any elements.
• Definition Classes
  • MapLike → GenMapLike

(defined at scala.collection.MapLike)

def newBuilder: Builder[(A, B), This]

A common implementation of newBuilder for all maps in terms of empty . Overridden for mutable maps in mutable.MapLike .

• Attributes
  • protected[this]
• Definition Classes
  • MapLike → TraversableLike → HasNewBuilder

(defined at scala.collection.MapLike)

def parCombiner: Combiner[(A, B), ParMap[A, B]]

The default par implementation uses the combiner provided by this method to create a new parallel collection.

• returns
  • a combiner for the parallel collection of type ParRepr
• Attributes
  • protected[this]
• Definition Classes
  • MapLike → TraversableLike → Parallelizable

(defined at scala.collection.MapLike)

def toBuffer[C >: (A, B)]: Buffer[C]

Uses the contents of this map to create a new mutable buffer.

• returns
  • a buffer containing all elements of this map.
• Definition Classes
  • MapLike → TraversableOnce → GenTraversableOnce

(defined at scala.collection.MapLike)

def updated[B1 >: B](key: A, value: B1): Map[A, B1]

[use case]

Creates a new map obtained by updating this map with a given key/value pair.

• key
  • the key
• value
  • the value
• returns
  • A new map with the new key/value mapping added to this map.

(defined at scala.collection.MapLike)

Concrete Value Members From scala.collection.Parallelizable

def par: ParMap[A, B]

Returns a parallel implementation of this collection.

For most collection types, this method creates a new parallel collection by copying all the elements. For these collection, par takes linear time. Mutable collections in this category do not produce a mutable parallel collection that has the same underlying dataset, so changes in one collection will not be reflected in the other one.

Specific collections (e.g. ParArray or mutable.ParHashMap ) override this default behaviour by creating a parallel collection which shares the same underlying dataset. For these collections, par takes constant or sublinear time.

All parallel collections return a reference to themselves.

• returns
  • a parallel implementation of this collection
• Definition Classes
  • Parallelizable

(defined at scala.collection.Parallelizable)

Concrete Value Members From scala.collection.TraversableLike

def ++:[B >: (A, B), That](that: Traversable[B])(implicit bf: CanBuildFrom[This, B, That]): That

As with ++ , returns a new collection containing the elements from the left operand followed by the elements from the right operand.

It differs from ++ in that the right operand determines the type of the resulting collection rather than the left one. Mnemonic: the COLon is on the side of the new COLlection type.

Example:

scala> val x = List(1)
x: List[Int] = List(1)

scala> val y = LinkedList(2)
y: scala.collection.mutable.LinkedList[Int] = LinkedList(2)

scala> val z = x ++: y
z: scala.collection.mutable.LinkedList[Int] = LinkedList(1, 2)

This overload exists because: for the implementation of ++: we should reuse that of ++ because many collections override it with more efficient versions.

Since TraversableOnce has no ++ method, we have to implement that directly, but Traversable and down can use the overload.

• B
  • the element type of the returned collection.
• That
  • the class of the returned collection. Where possible, That is the same class as the current collection class Repr , but this depends on the element type B being admissible for that class, which means that an implicit instance of type CanBuildFrom[Repr, B, That] is found.
• that
  • the traversable to append.
• bf
  • an implicit value of class CanBuildFrom which determines the result class That from the current representation type Repr and and the new element type B .
• returns
  • a new collection of type That which contains all elements of this traversable collection followed by all elements of that .
• Definition Classes
  • TraversableLike

(defined at scala.collection.TraversableLike)

def ++:[B >: (A, B), That](that: TraversableOnce[B])(implicit bf: CanBuildFrom[This, B, That]): That

[use case]

As with ++ , returns a new collection containing the elements from the left operand followed by the elements from the right operand.

It differs from ++ in that the right operand determines the type of the resulting collection rather than the left one. Mnemonic: the COLon is on the side of the new COLlection type.

Example:

scala> val x = List(1)
x: List[Int] = List(1)

scala> val y = LinkedList(2)
y: scala.collection.mutable.LinkedList[Int] = LinkedList(2)

scala> val z = x ++: y
z: scala.collection.mutable.LinkedList[Int] = LinkedList(1, 2)

• B
  • the element type of the returned collection.
• that
  • the traversable to append.
• returns
  • a new map which contains all elements of this map followed by all elements of that .
• Definition Classes
  • TraversableLike

(defined at scala.collection.TraversableLike)

def ++[B >: (A, B), That](that: GenTraversableOnce[B])(implicit bf: CanBuildFrom[This, B, That]): That

[use case]

Returns a new map containing the elements from the left hand operand followed by the elements from the right hand operand. The element type of the map is the most specific superclass encompassing the element types of the two operands.

Example:

scala> val a = List(1)
a: List[Int] = List(1)

scala> val b = List(2)
b: List[Int] = List(2)

scala> val c = a ++ b
c: List[Int] = List(1, 2)

scala> val d = List('a')
d: List[Char] = List(a)

scala> val e = c ++ d
e: List[AnyVal] = List(1, 2, a)

• B
  • the element type of the returned collection.
• that
  • the traversable to append.
• returns
  • a new map which contains all elements of this map followed by all elements of that .
• Definition Classes
  • TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableLike)

def collect[B, That](pf: PartialFunction[(A, B), B])(implicit bf: CanBuildFrom[This, B, That]): That

[use case]

Builds a new collection by applying a partial function to all elements of this map on which the function is defined.

• B
  • the element type of the returned collection.
• pf
  • the partial function which filters and maps the map.
• returns
  • a new map resulting from applying the given partial function pf to each element on which it is defined and collecting the results. The order of the elements is preserved.
• Definition Classes
  • TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableLike)

def dropWhile(p: ((A, B)) ⇒ Boolean): This

Drops longest prefix of elements that satisfy a predicate.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• returns
  • the longest suffix of this traversable collection whose first element does not satisfy the predicate p .
• Definition Classes
  • TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableLike)

def filter(p: ((A, B)) ⇒ Boolean): This

Selects all elements of this traversable collection which satisfy a predicate.

• p
  • the predicate used to test elements.
• returns
  • a new traversable collection consisting of all elements of this traversable collection that satisfy the given predicate p . The order of the elements is preserved.
• Definition Classes
  • TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableLike)

def flatMap[B, That](f: ((A, B)) ⇒ GenTraversableOnce[B])(implicit bf: CanBuildFrom[This, B, That]): That

[use case]

Builds a new collection by applying a function to all elements of this map and using the elements of the resulting collections.

For example:

def getWords(lines: Seq[String]): Seq[String] = lines flatMap (line => line split "\\W+")

The type of the resulting collection is guided by the static type of map. This might cause unexpected results sometimes. For example:

// lettersOf will return a Seq[Char] of likely repeated letters, instead of a Set
def lettersOf(words: Seq[String]) = words flatMap (word => word.toSet)

// lettersOf will return a Set[Char], not a Seq
def lettersOf(words: Seq[String]) = words.toSet flatMap (word => word.toSeq)

// xs will be an Iterable[Int]
val xs = Map("a" -> List(11,111), "b" -> List(22,222)).flatMap(_._2)

// ys will be a Map[Int, Int]
val ys = Map("a" -> List(1 -> 11,1 -> 111), "b" -> List(2 -> 22,2 -> 222)).flatMap(_._2)

• B
  • the element type of the returned collection.
• f
  • the function to apply to each element.
• returns
  • a new map resulting from applying the given collection-valued function f to each element of this map and concatenating the results.
• Definition Classes
  • TraversableLike → GenTraversableLike → FilterMonadic

(defined at scala.collection.TraversableLike)

def groupBy[K](f: ((A, B)) ⇒ K): immutable.Map[K, This]

Partitions this traversable collection into a map of traversable collections according to some discriminator function.

Note: this method is not re-implemented by views. This means when applied to a view it will always force the view and return a new traversable collection.

• K
  • the type of keys returned by the discriminator function.
• f
  • the discriminator function.
• returns
  • A map from keys to traversable collections such that the following invariant holds:

    (xs groupBy f)(k) = xs filter (x => f(x) == k)
    

That is, every key `k` is bound to a traversable collection of those
elements `x` for which `f(x)` equals `k` .

• Definition Classes
  • TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableLike)

def headOption: Option[(A, B)]

Optionally selects the first element.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• returns
  • the first element of this traversable collection if it is nonempty, None if it is empty.
• Definition Classes
  • TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableLike)

def init: This

Selects all elements except the last.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• returns
  • a traversable collection consisting of all elements of this traversable collection except the last one.
• Definition Classes
  • TraversableLike → GenTraversableLike
• Exceptions thrown
  • UnsupportedOperationException if the traversable collection is empty.

(defined at scala.collection.TraversableLike)

def inits: Iterator[This]

Iterates over the inits of this traversable collection. The first value will be this traversable collection and the final one will be an empty traversable collection, with the intervening values the results of successive applications of init .

• returns
  • an iterator over all the inits of this traversable collection
• Definition Classes
  • TraversableLike

Example:

List(1,2,3).inits = Iterator(List(1,2,3), List(1,2), List(1), Nil)

(defined at scala.collection.TraversableLike)

def last: (A, B)

Selects the last element.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• returns
  • The last element of this traversable collection.
• Definition Classes
  • TraversableLike → GenTraversableLike
• Exceptions thrown
  • NoSuchElementException If the traversable collection is empty.

(defined at scala.collection.TraversableLike)

def lastOption: Option[(A, B)]

Optionally selects the last element.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• returns
  • the last element of this traversable collection$ if it is nonempty, None if it is empty.
• Definition Classes
  • TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableLike)

def map[B, That](f: ((A, B)) ⇒ B)(implicit bf: CanBuildFrom[This, B, That]): That

[use case]

Builds a new collection by applying a function to all elements of this map.

• B
  • the element type of the returned collection.
• f
  • the function to apply to each element.
• returns
  • a new map resulting from applying the given function f to each element of this map and collecting the results.
• Definition Classes
  • TraversableLike → GenTraversableLike → FilterMonadic

(defined at scala.collection.TraversableLike)

def partition(p: ((A, B)) ⇒ Boolean): (This, This)

Partitions this traversable collection in two traversable collections according to a predicate.

• p
  • the predicate on which to partition.
• returns
  • a pair of traversable collections: the first traversable collection consists of all elements that satisfy the predicate p and the second traversable collection consists of all elements that don’t. The relative order of the elements in the resulting traversable collections is the same as in the original traversable collection.
• Definition Classes
  • TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableLike)

def repr: This

The collection of type traversable collection underlying this TraversableLike object. By default this is implemented as the TraversableLike object itself, but this can be overridden.

• Definition Classes
  • TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableLike)

def scanLeft[B, That](z: B)(op: (B, (A, B)) ⇒ B)(implicit bf: CanBuildFrom[This, B, That]): That

Produces a collection containing cumulative results of applying the operator going left to right.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• B
  • the type of the elements in the resulting collection
• That
  • the actual type of the resulting collection
• z
  • the initial value
• op
  • the binary operator applied to the intermediate result and the element
• bf
  • an implicit value of class CanBuildFrom which determines the result class That from the current representation type Repr and and the new element type B .
• returns
  • collection with intermediate results
• Definition Classes
  • TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableLike)

def scanRight[B, That](z: B)(op: ((A, B), B) ⇒ B)(implicit bf: CanBuildFrom[This, B, That]): That

Produces a collection containing cumulative results of applying the operator going right to left. The head of the collection is the last cumulative result.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered.

Example:

List(1, 2, 3, 4).scanRight(0)(_ + _) == List(10, 9, 7, 4, 0)

• B
  • the type of the elements in the resulting collection
• That
  • the actual type of the resulting collection
• z
  • the initial value
• op
  • the binary operator applied to the intermediate result and the element
• bf
  • an implicit value of class CanBuildFrom which determines the result class That from the current representation type Repr and and the new element type B .
• returns
  • collection with intermediate results
• Definition Classes
  • TraversableLike → GenTraversableLike
• Annotations
  • @migration
• Migration
  • (Changed in version 2.9.0) The behavior of scanRight has changed. The previous behavior can be reproduced with scanRight.reverse.

(defined at scala.collection.TraversableLike)

def scan[B >: (A, B), That](z: B)(op: (B, B) ⇒ B)(implicit cbf: CanBuildFrom[This, B, That]): That

Computes a prefix scan of the elements of the collection.

Note: The neutral element z may be applied more than once.

• B
  • element type of the resulting collection
• That
  • type of the resulting collection
• z
  • neutral element for the operator op
• op
  • the associative operator for the scan
• cbf
  • combiner factory which provides a combiner
• returns
  • a new traversable collection containing the prefix scan of the elements in this traversable collection
• Definition Classes
  • TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableLike)

def span(p: ((A, B)) ⇒ Boolean): (This, This)

Splits this traversable collection into a prefix/suffix pair according to a predicate.

Note: c span p is equivalent to (but possibly more efficient than) (c takeWhile p, c dropWhile p) , provided the evaluation of the predicate p does not cause any side-effects.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• returns
  • a pair consisting of the longest prefix of this traversable collection whose elements all satisfy p , and the rest of this traversable collection.
• Definition Classes
  • TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableLike)

def splitAt(n: Int): (This, This)

Splits this traversable collection into two at a given position. Note: c splitAt n is equivalent to (but possibly more efficient than) (c take n, c drop n) .

Note: might return different results for different runs, unless the underlying collection type is ordered.

• n
  • the position at which to split.
• returns
  • a pair of traversable collections consisting of the first n elements of this traversable collection, and the other elements.
• Definition Classes
  • TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableLike)

def tail: This

Selects all elements except the first.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• returns
  • a traversable collection consisting of all elements of this traversable collection except the first one.
• Definition Classes
  • TraversableLike → GenTraversableLike
• Exceptions thrown
  • UnsupportedOperationException if the traversable collection is empty.

(defined at scala.collection.TraversableLike)

def tails: Iterator[This]

Iterates over the tails of this traversable collection. The first value will be this traversable collection and the final one will be an empty traversable collection, with the intervening values the results of successive applications of tail .

• returns
  • an iterator over all the tails of this traversable collection
• Definition Classes
  • TraversableLike

Example:

List(1,2,3).tails = Iterator(List(1,2,3), List(2,3), List(3), Nil)

(defined at scala.collection.TraversableLike)

def toTraversable: Traversable[(A, B)]

Converts this traversable collection to an unspecified Traversable. Will return the same collection if this instance is already Traversable.

Note: will not terminate for infinite-sized collections.

• returns
  • a Traversable containing all elements of this traversable collection.
• Definition Classes
  • TraversableLike → TraversableOnce → GenTraversableOnce
• Annotations
  • @ deprecatedOverriding (message =…, since = “2.11.0”)

(defined at scala.collection.TraversableLike)

def withFilter(p: ((A, B)) ⇒ Boolean): FilterMonadic[(A, B), This]

Creates a non-strict filter of this traversable collection.

Note: the difference between c filter p and c withFilter p is that the former creates a new collection, whereas the latter only restricts the domain of subsequent map , flatMap , foreach , and withFilter operations.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• p
  • the predicate used to test elements.
• returns
  • an object of class WithFilter , which supports map , flatMap , foreach , and withFilter operations. All these operations apply to those elements of this traversable collection which satisfy the predicate p .
• Definition Classes
  • TraversableLike → FilterMonadic

(defined at scala.collection.TraversableLike)

Concrete Value Members From scala.collection.TraversableOnce

def /:[B](z: B)(op: (B, (A, B)) ⇒ B): B

Applies a binary operator to a start value and all elements of this traversable or iterator, going left to right.

Note: /: is alternate syntax for foldLeft ; z /: xs is the same as xs foldLeft z .

Examples:

Note that the folding function used to compute b is equivalent to that used to compute c.

scala> val a = List(1,2,3,4)
a: List[Int] = List(1, 2, 3, 4)

scala> val b = (5 /: a)(_+_)
b: Int = 15

scala> val c = (5 /: a)((x,y) => x + y)
c: Int = 15

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

• B
  • the result type of the binary operator.
• z
  • the start value.
• op
  • the binary operator.
• returns
  • the result of inserting op between consecutive elements of this traversable or iterator, going left to right with the start value z on the left:

    op(...op(op(z, x_1), x_2), ..., x_n)
    

where `x1, ..., xn` are the elements of this traversable or iterator.

• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def :\[B](z: B)(op: ((A, B), B) ⇒ B): B

Applies a binary operator to all elements of this traversable or iterator and a start value, going right to left.

Note: :\ is alternate syntax for foldRight ; xs :\ z is the same as xs foldRight z .

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

Examples:

Note that the folding function used to compute b is equivalent to that used to compute c.

scala> val a = List(1,2,3,4)
a: List[Int] = List(1, 2, 3, 4)

scala> val b = (a :\ 5)(_+_)
b: Int = 15

scala> val c = (a :\ 5)((x,y) => x + y)
c: Int = 15

• B
  • the result type of the binary operator.
• z
  • the start value
• op
  • the binary operator
• returns
  • the result of inserting op between consecutive elements of this traversable or iterator, going right to left with the start value z on the right:

    op(x_1, op(x_2, ... op(x_n, z)...))
    

where `x1, ..., xn` are the elements of this traversable or iterator.

• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def addString(b: StringBuilder): StringBuilder

Appends all elements of this traversable or iterator to a string builder. The written text consists of the string representations (w.r.t. the method toString ) of all elements of this traversable or iterator without any separator string.

Example:

scala> val a = List(1,2,3,4)
a: List[Int] = List(1, 2, 3, 4)

scala> val b = new StringBuilder()
b: StringBuilder =

scala> val h = a.addString(b)
h: StringBuilder = 1234

• b
  • the string builder to which elements are appended.
• returns
  • the string builder b to which elements were appended.
• Definition Classes
  • TraversableOnce

(defined at scala.collection.TraversableOnce)

def addString(b: StringBuilder, sep: String): StringBuilder

Appends all elements of this traversable or iterator to a string builder using a separator string. The written text consists of the string representations (w.r.t. the method toString ) of all elements of this traversable or iterator, separated by the string sep .

Example:

scala> val a = List(1,2,3,4)
a: List[Int] = List(1, 2, 3, 4)

scala> val b = new StringBuilder()
b: StringBuilder =

scala> a.addString(b, ", ")
res0: StringBuilder = 1, 2, 3, 4

• b
  • the string builder to which elements are appended.
• sep
  • the separator string.
• returns
  • the string builder b to which elements were appended.
• Definition Classes
  • TraversableOnce

(defined at scala.collection.TraversableOnce)

def aggregate[B](z: ⇒ B)(seqop: (B, (A, B)) ⇒ B, combop: (B, B) ⇒ B): B

Aggregates the results of applying an operator to subsequent elements.

This is a more general form of fold and reduce . It is similar to foldLeft in that it doesn’t require the result to be a supertype of the element type. In addition, it allows parallel collections to be processed in chunks, and then combines the intermediate results.

aggregate splits the traversable or iterator into partitions and processes each partition by sequentially applying seqop , starting with z (like foldLeft ). Those intermediate results are then combined by using combop (like fold ). The implementation of this operation may operate on an arbitrary number of collection partitions (even 1), so combop may be invoked an arbitrary number of times (even 0).

As an example, consider summing up the integer values of a list of chars. The initial value for the sum is 0. First, seqop transforms each input character to an Int and adds it to the sum (of the partition). Then, combop just needs to sum up the intermediate results of the partitions:

List('a', 'b', 'c').aggregate(0)({ (sum, ch) => sum + ch.toInt }, { (p1, p2) => p1 + p2 })

• B
  • the type of accumulated results
• z
  • the initial value for the accumulated result of the partition - this will typically be the neutral element for the seqop operator (e.g. Nil for list concatenation or 0 for summation) and may be evaluated more than once
• seqop
  • an operator used to accumulate results within a partition
• combop
  • an associative operator used to combine results from different partitions
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def collectFirst[B](pf: PartialFunction[(A, B), B]): Option[B]

Finds the first element of the traversable or iterator for which the given partial function is defined, and applies the partial function to it.

Note: may not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• pf
  • the partial function
• returns
  • an option value containing pf applied to the first value for which it is defined, or None if none exists.
• Definition Classes
  • TraversableOnce

Example:

Seq("a", 1, 5L).collectFirst({ case x: Int => x*10 }) = Some(10)

(defined at scala.collection.TraversableOnce)

def copyToArray[B >: (A, B)](xs: Array[B]): Unit

[use case]

Copies the elements of this map to an array. Fills the given array xs with values of this map. Copying will stop once either the end of the current map is reached, or the end of the target array is reached.

• xs
  • the array to fill.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def copyToArray[B >: (A, B)](xs: Array[B], start: Int): Unit

[use case]

Copies the elements of this map to an array. Fills the given array xs with values of this map, beginning at index start . Copying will stop once either the end of the current map is reached, or the end of the target array is reached.

• xs
  • the array to fill.
• start
  • the starting index.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def copyToBuffer[B >: (A, B)](dest: Buffer[B]): Unit

Copies all elements of this traversable or iterator to a buffer.

Note: will not terminate for infinite-sized collections.

• dest
  • The buffer to which elements are copied.
• Definition Classes
  • TraversableOnce

(defined at scala.collection.TraversableOnce)

def count(p: ((A, B)) ⇒ Boolean): Int

Counts the number of elements in the traversable or iterator which satisfy a predicate.

• p
  • the predicate used to test elements.
• returns
  • the number of elements satisfying the predicate p .
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def foldLeft[B](z: B)(op: (B, (A, B)) ⇒ B): B

Applies a binary operator to a start value and all elements of this traversable or iterator, going left to right.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

• B
  • the result type of the binary operator.
• z
  • the start value.
• op
  • the binary operator.
• returns
  • the result of inserting op between consecutive elements of this traversable or iterator, going left to right with the start value z on the left:

    op(...op(z, x_1), x_2, ..., x_n)
    

where `x1, ..., xn` are the elements of this traversable or iterator.
Returns `z` if this traversable or iterator is empty.

• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def fold[A1 >: (A, B)](z: A1)(op: (A1, A1) ⇒ A1): A1

Folds the elements of this traversable or iterator using the specified associative binary operator.

The order in which operations are performed on elements is unspecified and may be nondeterministic.

Note: will not terminate for infinite-sized collections.

• A1
  • a type parameter for the binary operator, a supertype of A .
• z
  • a neutral element for the fold operation; may be added to the result an arbitrary number of times, and must not change the result (e.g., Nil for list concatenation, 0 for addition, or 1 for multiplication).
• op
  • a binary operator that must be associative.
• returns
  • the result of applying the fold operator op between all the elements and z , or z if this traversable or iterator is empty.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def maxBy[B](f: ((A, B)) ⇒ B)(implicit cmp: Ordering[B]): (A, B)

[use case]

Finds the first element which yields the largest value measured by function f.

• B
  • The result type of the function f.
• f
  • The measuring function.
• returns
  • the first element of this map with the largest value measured by function f.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def minBy[B](f: ((A, B)) ⇒ B)(implicit cmp: Ordering[B]): (A, B)

[use case]

Finds the first element which yields the smallest value measured by function f.

• B
  • The result type of the function f.
• f
  • The measuring function.
• returns
  • the first element of this map with the smallest value measured by function f.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def mkString(sep: String): String

Displays all elements of this traversable or iterator in a string using a separator string.

• sep
  • the separator string.
• returns
  • a string representation of this traversable or iterator. In the resulting string the string representations (w.r.t. the method toString ) of all elements of this traversable or iterator are separated by the string sep .
• Definition Classes
  • TraversableOnce → GenTraversableOnce

Example:

List(1, 2, 3).mkString("|") = "1|2|3"

(defined at scala.collection.TraversableOnce)

def mkString(start: String, sep: String, end: String): String

Displays all elements of this traversable or iterator in a string using start, end, and separator strings.

• start
  • the starting string.
• sep
  • the separator string.
• end
  • the ending string.
• returns
  • a string representation of this traversable or iterator. The resulting string begins with the string start and ends with the string end . Inside, the string representations (w.r.t. the method toString ) of all elements of this traversable or iterator are separated by the string sep .
• Definition Classes
  • TraversableOnce → GenTraversableOnce

Example:

List(1, 2, 3).mkString("(", "; ", ")") = "(1; 2; 3)"

(defined at scala.collection.TraversableOnce)

def reduceLeftOption[B >: (A, B)](op: (B, (A, B)) ⇒ B): Option[B]

Optionally applies a binary operator to all elements of this traversable or iterator, going left to right.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

• B
  • the result type of the binary operator.
• op
  • the binary operator.
• returns
  • an option value containing the result of reduceLeft(op) if this traversable or iterator is nonempty, None otherwise.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def reduceLeft[B >: (A, B)](op: (B, (A, B)) ⇒ B): B

Applies a binary operator to all elements of this traversable or iterator, going left to right.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

• B
  • the result type of the binary operator.
• op
  • the binary operator.
• returns
  • the result of inserting op between consecutive elements of this traversable or iterator, going left to right:

    op( op( ... op(x_1, x_2) ..., x_{n-1}), x_n)
    

where `x1, ..., xn` are the elements of this traversable or iterator.

• Definition Classes
  • TraversableOnce
• Exceptions thrown
  • UnsupportedOperationException if this traversable or iterator is empty.

(defined at scala.collection.TraversableOnce)

def reduceOption[A1 >: (A, B)](op: (A1, A1) ⇒ A1): Option[A1]

Reduces the elements of this traversable or iterator, if any, using the specified associative binary operator.

The order in which operations are performed on elements is unspecified and may be nondeterministic.

• A1
  • A type parameter for the binary operator, a supertype of A .
• op
  • A binary operator that must be associative.
• returns
  • An option value containing result of applying reduce operator op between all the elements if the collection is nonempty, and None otherwise.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def reduceRightOption[B >: (A, B)](op: ((A, B), B) ⇒ B): Option[B]

Optionally applies a binary operator to all elements of this traversable or iterator, going right to left.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

• B
  • the result type of the binary operator.
• op
  • the binary operator.
• returns
  • an option value containing the result of reduceRight(op) if this traversable or iterator is nonempty, None otherwise.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def reduce[A1 >: (A, B)](op: (A1, A1) ⇒ A1): A1

Reduces the elements of this traversable or iterator using the specified associative binary operator.

The order in which operations are performed on elements is unspecified and may be nondeterministic.

• A1
  • A type parameter for the binary operator, a supertype of A .
• op
  • A binary operator that must be associative.
• returns
  • The result of applying reduce operator op between all the elements if the traversable or iterator is nonempty.
• Definition Classes
  • TraversableOnce → GenTraversableOnce
• Exceptions thrown
  • UnsupportedOperationException if this traversable or iterator is empty.

(defined at scala.collection.TraversableOnce)

def reversed: List[(A, B)]

• Attributes
  • protected[this]
• Definition Classes
  • TraversableOnce

(defined at scala.collection.TraversableOnce)

def toIndexedSeq: immutable.IndexedSeq[(A, B)]

Converts this traversable or iterator to an indexed sequence.

Note: will not terminate for infinite-sized collections.

• returns
  • an indexed sequence containing all elements of this traversable or iterator.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def toList: List[(A, B)]

Converts this traversable or iterator to a list.

Note: will not terminate for infinite-sized collections.

• returns
  • a list containing all elements of this traversable or iterator.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def toMap[T, U](implicit ev: <:<[(A, B), (T, U)]): immutable.Map[T, U]

[use case]

Converts this map to a map. This method is unavailable unless the elements are members of Tuple2, each ((T, U)) becoming a key-value pair in the map. Duplicate keys will be overwritten by later keys: if this is an unordered collection, which key is in the resulting map is undefined.

• returns
  • a map of type immutable.Map[T, U] containing all key/value pairs of type (T, U) of this map.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def toSet[B >: (A, B)]: immutable.Set[B]

Converts this traversable or iterator to a set.

Note: will not terminate for infinite-sized collections.

• returns
  • a set containing all elements of this traversable or iterator.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def toVector: Vector[(A, B)]

Converts this traversable or iterator to a Vector.

Note: will not terminate for infinite-sized collections.

• returns
  • a vector containing all elements of this traversable or iterator.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

Concrete Value Members From scala.collection.generic.Subtractable

def -(elem1: A, elem2: A, elems: A*): This

Creates a new collection from this collection with some elements removed.

This method takes two or more elements to be removed. Another overloaded variant of this method handles the case where a single element is removed.

• elem1
  • the first element to remove.
• elem2
  • the second element to remove.
• elems
  • the remaining elements to remove.
• returns
  • a new collection that contains all elements of the current collection except one less occurrence of each of the given elements.
• Definition Classes
  • Subtractable

(defined at scala.collection.generic.Subtractable)

def --(xs: GenTraversableOnce[A]): This

Creates a new collection from this collection by removing all elements of another collection.

• xs
  • the collection containing the removed elements.
• returns
  • a new collection that contains all elements of the current collection except one less occurrence of each of the elements of elems .
• Definition Classes
  • Subtractable

(defined at scala.collection.generic.Subtractable)

Concrete Value Members From Implicit scala.collection.parallel.CollectionsHaveToParArray ——————————————————————————–

def toParArray: ParArray[T]

• Implicit information
  • This member is added by an implicit conversion from MapLike [A, B, This] to CollectionsHaveToParArray [MapLike [A, B, This], T] performed by method CollectionsHaveToParArray in scala.collection.parallel. This conversion will take place only if an implicit value of type (MapLike [A, B, This]) ⇒ GenTraversableOnce [T] is in scope.
• Definition Classes
  • CollectionsHaveToParArray (added by implicit convertion: scala.collection.parallel.CollectionsHaveToParArray)

Full Source:

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2003-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

package scala
package collection

import generic._
import mutable.{ Builder, MapBuilder }
import scala.annotation.migration
import parallel.ParMap

/** A template trait for maps, which associate keys with values.
 *
 *  $mapNote
 *  $mapTags
 *  @since 2.8
 *
 *  @define mapNote
 *    '''Implementation note:'''
 *    This trait provides most of the operations of a `Map` independently of its representation.
 *    It is typically inherited by concrete implementations of maps.
 *
 *    To implement a concrete map, you need to provide implementations of the
 *    following methods:
 *    {{{
 *       def get(key: A): Option[B]
 *       def iterator: Iterator[(A, B)]
 *       def + [B1 >: B](kv: (A, B1)): This
 *       def -(key: A): This
 *    }}}
 *    If you wish that methods like `take`, `drop`, `filter` also return the same kind of map
 *    you should also override:
 *    {{{
 *       def empty: This
 *    }}}
 *    It is also good idea to override methods `foreach` and
 *    `size` for efficiency.
 *
 *  @define mapTags
 *  @tparam A    the type of the keys.
 *  @tparam B    the type of associated values.
 *  @tparam This the type of the map itself.
 *
 *  @author  Martin Odersky
 *  @version 2.8
 *
 *  @define coll map
 *  @define Coll Map
 *  @define willNotTerminateInf
 *  @define mayNotTerminateInf
 */
trait MapLike[A, +B, +This <: MapLike[A, B, This] with Map[A, B]]
  extends PartialFunction[A, B]
     with IterableLike[(A, B), This]
     with GenMapLike[A, B, This]
     with Subtractable[A, This]
     with Parallelizable[(A, B), ParMap[A, B]]
{
self =>

  /** The empty map of the same type as this map
   *   @return   an empty map of type `This`.
   */
  def empty: This

  /** A common implementation of `newBuilder` for all maps in terms of `empty`.
   *  Overridden for mutable maps in `mutable.MapLike`.
   */
  override protected[this] def newBuilder: Builder[(A, B), This] = new MapBuilder[A, B, This](empty)

  /** Optionally returns the value associated with a key.
   *
   *  @param  key    the key value
   *  @return an option value containing the value associated with `key` in this map,
   *          or `None` if none exists.
   */
  def get(key: A): Option[B]

  /** Creates a new iterator over all key/value pairs of this map
   *
   *  @return the new iterator
   */
  def iterator: Iterator[(A, B)]

  /** Adds a key/value pair to this map, returning a new map.
   *  @param    kv the key/value pair
   *  @tparam   B1 the type of the value in the key/value pair.
   *  @return   a new map with the new binding added to this map
   *
   *  @usecase  def + (kv: (A, B)): Map[A, B]
   *    @inheritdoc
   */
  def + [B1 >: B] (kv: (A, B1)): Map[A, B1]

  /** Removes a key from this map, returning a new map.
   *  @param    key the key to be removed
   *  @return   a new map without a binding for `key`
   *
   *  @usecase  def - (key: A): Map[A, B]
   *    @inheritdoc
   */
  def - (key: A): This

  /** Tests whether the map is empty.
   *
   *  @return `true` if the map does not contain any key/value binding, `false` otherwise.
   */
  override def isEmpty: Boolean = size == 0

  /**  Returns the value associated with a key, or a default value if the key is not contained in the map.
   *   @param   key      the key.
   *   @param   default  a computation that yields a default value in case no binding for `key` is
   *                     found in the map.
   *   @tparam  B1       the result type of the default computation.
   *   @return  the value associated with `key` if it exists,
   *            otherwise the result of the `default` computation.
   *
   *   @usecase def getOrElse(key: A, default: => B): B
   *     @inheritdoc
   */
  def getOrElse[B1 >: B](key: A, default: => B1): B1 = get(key) match {
    case Some(v) => v
    case None => default
  }

  /** Retrieves the value which is associated with the given key. This
   *  method invokes the `default` method of the map if there is no mapping
   *  from the given key to a value. Unless overridden, the `default` method throws a
   *  `NoSuchElementException`.
   *
   *  @param  key the key
   *  @return     the value associated with the given key, or the result of the
   *              map's `default` method, if none exists.
   */
  def apply(key: A): B = get(key) match {
    case None => default(key)
    case Some(value) => value
  }

  /** Tests whether this map contains a binding for a key.
   *
   *  @param key the key
   *  @return    `true` if there is a binding for `key` in this map, `false` otherwise.
   */
  def contains(key: A): Boolean = get(key).isDefined

  /** Tests whether this map contains a binding for a key. This method,
   *  which implements an abstract method of trait `PartialFunction`,
   *  is equivalent to `contains`.
   *
   *  @param key the key
   *  @return    `true` if there is a binding for `key` in this map, `false` otherwise.
   */
  def isDefinedAt(key: A) = contains(key)

  /** Collects all keys of this map in a set.
   * @return  a set containing all keys of this map.
   */
  def keySet: Set[A] = new DefaultKeySet

  /** The implementation class of the set returned by `keySet`.
   */
  protected class DefaultKeySet extends AbstractSet[A] with Set[A] with Serializable {
    def contains(key : A) = self.contains(key)
    def iterator = keysIterator
    def + (elem: A): Set[A] = (Set[A]() ++ this + elem).asInstanceOf[Set[A]] // !!! concrete overrides abstract problem
    def - (elem: A): Set[A] = (Set[A]() ++ this - elem).asInstanceOf[Set[A]] // !!! concrete overrides abstract problem
    override def size = self.size
    override def foreach[U](f: A => U) = self.keysIterator foreach f
  }

  /** Creates an iterator for all keys.
   *
   *  @return an iterator over all keys.
   */
  def keysIterator: Iterator[A] = new AbstractIterator[A] {
    val iter = self.iterator
    def hasNext = iter.hasNext
    def next() = iter.next()._1
  }

  /** Collects all keys of this map in an iterable collection.
   *
   *  @return the keys of this map as an iterable.
   */
  @migration("`keys` returns `Iterable[A]` rather than `Iterator[A]`.", "2.8.0")
  def keys: Iterable[A] = keySet

  /** Collects all values of this map in an iterable collection.
   *
   *  @return the values of this map as an iterable.
   */
  @migration("`values` returns `Iterable[B]` rather than `Iterator[B]`.", "2.8.0")
  def values: Iterable[B] = new DefaultValuesIterable

  /** The implementation class of the iterable returned by `values`.
   */
  protected class DefaultValuesIterable extends AbstractIterable[B] with Iterable[B] with Serializable {
    def iterator = valuesIterator
    override def size = self.size
    override def foreach[U](f: B => U) = self.valuesIterator foreach f
  }

  /** Creates an iterator for all values in this map.
   *
   *  @return an iterator over all values that are associated with some key in this map.
   */
  def valuesIterator: Iterator[B] = new AbstractIterator[B] {
    val iter = self.iterator
    def hasNext = iter.hasNext
    def next() = iter.next()._2
  }

  /** Defines the default value computation for the map,
   *  returned when a key is not found
   *  The method implemented here throws an exception,
   *  but it might be overridden in subclasses.
   *
   *  @param key the given key value for which a binding is missing.
   *  @throws NoSuchElementException
   */
  def default(key: A): B =
    throw new NoSuchElementException("key not found: " + key)

  protected class FilteredKeys(p: A => Boolean) extends AbstractMap[A, B] with DefaultMap[A, B] {
    override def foreach[U](f: ((A, B)) => U): Unit = for (kv <- self) if (p(kv._1)) f(kv)
    def iterator = self.iterator.filter(kv => p(kv._1))
    override def contains(key: A) = p(key) && self.contains(key)
    def get(key: A) = if (!p(key)) None else self.get(key)
  }

  /** Filters this map by retaining only keys satisfying a predicate.
   *
   *  '''Note''': the predicate must accept any key of type `A`, not just those already
   *  present in the map, as the predicate is tested before the underlying map is queried.
   *
   *  @param  p   the predicate used to test keys
   *  @return an immutable map consisting only of those key value pairs of this map where the key satisfies
   *          the predicate `p`. The resulting map wraps the original map without copying any elements.
   */
  def filterKeys(p: A => Boolean): Map[A, B] = new FilteredKeys(p)

  protected class MappedValues[C](f: B => C) extends AbstractMap[A, C] with DefaultMap[A, C] {
    override def foreach[U](g: ((A, C)) => U): Unit = for ((k, v) <- self) g((k, f(v)))
    def iterator = for ((k, v) <- self.iterator) yield (k, f(v))
    override def size = self.size
    override def contains(key: A) = self.contains(key)
    def get(key: A) = self.get(key).map(f)
  }

  /** Transforms this map by applying a function to every retrieved value.
   *  @param  f   the function used to transform values of this map.
   *  @return a map view which maps every key of this map
   *          to `f(this(key))`. The resulting map wraps the original map without copying any elements.
   */
  def mapValues[C](f: B => C): Map[A, C] = new MappedValues(f)

  // The following 5 operations (updated, two times +, two times ++) should really be
  // generic, returning This[B]. We need better covariance support to express that though.
  // So right now we do the brute force approach of code duplication.

  /** Creates a new map obtained by updating this map with a given key/value pair.
   *  @param    key the key
   *  @param    value the value
   *  @tparam   B1 the type of the added value
   *  @return   A new map with the new key/value mapping added to this map.
   *
   *  @usecase  def updated(key: A, value: B): Map[A, B]
   *    @inheritdoc
   */
  def updated [B1 >: B](key: A, value: B1): Map[A, B1] = this + ((key, value))

  /** Adds key/value pairs to this map, returning a new map.
   *
   *  This method takes two or more key/value pairs. Another overloaded
   *  variant of this method handles the case where a single key/value pair is
   *  added.
   *  @param    kv1 the first key/value pair
   *  @param    kv2 the second key/value pair
   *  @param    kvs the remaining key/value pairs
   *  @tparam   B1  the type of the added values
   *  @return   a new map with the given bindings added to this map
   *
   *  @usecase  def + (kvs: (A, B)*): Map[A, B]
   *    @inheritdoc
   *    @param    kvs the key/value pairs
   */
  def + [B1 >: B] (kv1: (A, B1), kv2: (A, B1), kvs: (A, B1) *): Map[A, B1] =
    this + kv1 + kv2 ++ kvs

  /** Adds all key/value pairs in a traversable collection to this map, returning a new map.
   *
   *  @param    xs  the collection containing the added key/value pairs
   *  @tparam   B1  the type of the added values
   *  @return   a new map with the given bindings added to this map
   *
   *  @usecase  def ++ (xs: Traversable[(A, B)]): Map[A, B]
   *    @inheritdoc
   */
  def ++[B1 >: B](xs: GenTraversableOnce[(A, B1)]): Map[A, B1] =
    ((repr: Map[A, B1]) /: xs.seq) (_ + _)

  /** Returns a new map obtained by removing all key/value pairs for which the predicate
   *  `p` returns `true`.
   *
   *  '''Note:'''    This method works by successively removing elements for which the
   *           predicate is true from this set.
   *           If removal is slow, or you expect that most elements of the set
   *           will be removed, you might consider using `filter`
   *           with a negated predicate instead.
   *  @param p    A predicate over key-value pairs
   *  @return     A new map containing elements not satisfying the predicate.
   */
  override def filterNot(p: ((A, B)) => Boolean): This = {
    var res: This = repr
    for (kv <- this)
      if (p(kv)) res = (res - kv._1).asInstanceOf[This] // !!! concrete overrides abstract problem
    res
  }

  override def toSeq: Seq[(A, B)] = {
    if (isEmpty) Vector.empty[(A, B)]
    else {
      // Default appropriate for immutable collections; mutable collections override this
      val vb = Vector.newBuilder[(A, B)]
      foreach(vb += _)
      vb.result
    }
  }

  override def toBuffer[C >: (A, B)]: mutable.Buffer[C] = {
    val result = new mutable.ArrayBuffer[C](size)
    // Faster to let the map iterate itself than to defer through copyToBuffer
    foreach(result += _)
    result
  }

  protected[this] override def parCombiner = ParMap.newCombiner[A, B]

  /** Appends all bindings of this map to a string builder using start, end, and separator strings.
   *  The written text begins with the string `start` and ends with the string
   *  `end`. Inside, the string representations of all bindings of this map
   *  in the form of `key -> value` are separated by the string `sep`.
   *
   *  @param b     the builder to which strings are appended.
   *  @param start the starting string.
   *  @param sep   the separator string.
   *  @param end   the ending string.
   *  @return      the string builder `b` to which elements were appended.
   */
  override def addString(b: StringBuilder, start: String, sep: String, end: String): StringBuilder =
    this.iterator.map { case (k, v) => k+" -> "+v }.addString(b, start, sep, end)

  /** Defines the prefix of this object's `toString` representation.
   *  @return  a string representation which starts the result of `toString` applied to this $coll.
   *           Unless overridden in subclasses, the string prefix of every map is `"Map"`.
   */
  override def stringPrefix: String = "Map"

  override /*PartialFunction*/
  def toString = super[IterableLike].toString

}