scala.collection.GenTraversableLike

trait GenTraversableLike[+A, +Repr] extends GenTraversableOnce[A] with Parallelizable[A, ParIterable[A]]

A template trait for all traversable collections upon which operations may be implemented in parallel.

Abstract Value Members From scala.collection.GenTraversableLike

abstract def drop(n: Int): Repr

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 general collection.
  • returns
    • a general collection consisting of all elements of this general collection except the first n ones, or else the empty general collection, if this general collection has less than n elements.

(defined at scala.collection.GenTraversableLike)

abstract def dropWhile(pred: (A) ⇒ Boolean): Repr

Drops longest prefix of elements that satisfy a predicate.

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

  • pred
    • The predicate used to test elements.
  • returns
    • the longest suffix of this general collection whose first element does not satisfy the predicate p .

(defined at scala.collection.GenTraversableLike)

abstract def filter(pred: (A) ⇒ Boolean): Repr

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

  • pred
    • the predicate used to test elements.
  • returns
    • a new general collection consisting of all elements of this general collection that satisfy the given predicate p . Their order may not be preserved.

(defined at scala.collection.GenTraversableLike)

abstract def filterNot(pred: (A) ⇒ Boolean): Repr

Selects all elements of this general collection which do not satisfy a predicate.

  • pred
    • the predicate used to test elements.
  • returns
    • a new general collection consisting of all elements of this general collection that do not satisfy the given predicate p . Their order may not be preserved.

(defined at scala.collection.GenTraversableLike)

abstract def groupBy[K](f: (A) ⇒ K): GenMap[K, Repr]

Partitions this general collection into a map of general 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 general collection.

  • K
    • the type of keys returned by the discriminator function.
  • f
    • the discriminator function.
  • returns
    • A map from keys to general 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 general collection of those elements
 `x` for which `f(x)` equals `k` .

(defined at scala.collection.GenTraversableLike)

abstract def partition(pred: (A) ⇒ Boolean): (Repr, Repr)

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

  • pred
    • the predicate on which to partition.
  • returns
    • a pair of general collections: the first general collection consists of all elements that satisfy the predicate p and the second general collection consists of all elements that don’t. The relative order of the elements in the resulting general collections may not be preserved.

(defined at scala.collection.GenTraversableLike)

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

(defined at scala.collection.GenTraversableLike)

abstract def scanRight[B, That](z: B)(op: (A, B) ⇒ B)(implicit bf: CanBuildFrom[Repr, 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
  • 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.GenTraversableLike)

abstract def scan[B >: A, That](z: B)(op: (B, B) ⇒ B)(implicit cbf: CanBuildFrom[Repr, 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 general collection containing the prefix scan of the elements in this general collection

(defined at scala.collection.GenTraversableLike)

abstract def slice(unc_from: Int, unc_until: Int): Repr

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.

  • unc_from
    • the lowest index to include from this general collection.
  • unc_until
    • the lowest index to EXCLUDE from this general collection.
  • returns
    • a general collection containing the elements greater than or equal to index from extending up to (but not including) index until of this general collection.

(defined at scala.collection.GenTraversableLike)

abstract def span(pred: (A) ⇒ Boolean): (Repr, Repr)

Splits this general 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.

  • pred
    • the test predicate
  • returns
    • a pair consisting of the longest prefix of this general collection whose elements all satisfy p , and the rest of this general collection.

(defined at scala.collection.GenTraversableLike)

abstract def splitAt(n: Int): (Repr, Repr)

Splits this general 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 general collections consisting of the first n elements of this general collection, and the other elements.

(defined at scala.collection.GenTraversableLike)

abstract def take(n: Int): Repr

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 general collection.
  • returns
    • a general collection consisting only of the first n elements of this general collection, or else the whole general collection, if it has less than n elements.

(defined at scala.collection.GenTraversableLike)

abstract def takeWhile(pred: (A) ⇒ Boolean): Repr

Takes longest prefix of elements that satisfy a predicate.

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

  • pred
    • The predicate used to test elements.
  • returns
    • the longest prefix of this general collection whose elements all satisfy the predicate p .

(defined at scala.collection.GenTraversableLike)

Concrete Value Members From scala.collection.GenTraversableLike

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

[use case]

Returns a new general collection containing the elements from the left hand operand followed by the elements from the right hand operand. The element type of the general collection 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 general collection which contains all elements of this general collection followed by all elements of that .

(defined at scala.collection.GenTraversableLike)

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

[use case]

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

  • B
    • the element type of the returned collection.
  • pf
    • the partial function which filters and maps the general collection.
  • returns
    • a new general collection 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.

(defined at scala.collection.GenTraversableLike)

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

[use case]

Builds a new collection by applying a function to all elements of this general collection 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 general collection. 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 general collection resulting from applying the given collection-valued function f to each element of this general collection and concatenating the results.

(defined at scala.collection.GenTraversableLike)

abstract def foreach[U](f: (A) ⇒ U): Unit

[use case]

Applies a function f to all elements of this general collection.

Note: this method underlies the implementation of most other bulk operations. It’s important to implement this method in an efficient way.

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

(defined at scala.collection.GenTraversableLike)

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

[use case]

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

  • B
    • the element type of the returned collection.
  • f
    • the function to apply to each element.
  • returns
    • a new general collection resulting from applying the given function f to each element of this general collection and collecting the results.

(defined at scala.collection.GenTraversableLike)

Abstract Value Members From scala.collection.GenTraversableOnce

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

Applies a binary operator to a start value and all elements of this collection 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 collection 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 collection or iterator.
  • Definition Classes
    • GenTraversableOnce

(defined at scala.collection.GenTraversableOnce)

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

Applies a binary operator to all elements of this collection 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 collection 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 collection or iterator.
  • Definition Classes
    • GenTraversableOnce

(defined at scala.collection.GenTraversableOnce)

abstract def aggregate[B](z: ⇒ B)(seqop: (B, A) ⇒ 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 collection 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
    • GenTraversableOnce

(defined at scala.collection.GenTraversableOnce)

abstract def count(p: (A) ⇒ Boolean): Int

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

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

(defined at scala.collection.GenTraversableOnce)

abstract def exists(p: (A) ⇒ Boolean): Boolean

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

Note: may not terminate for infinite-sized collections.

  • p
    • the predicate used to test elements.
  • returns
    • true if the given predicate p is satisfied by at least one element of this collection or iterator, otherwise false
  • Definition Classes
    • GenTraversableOnce

(defined at scala.collection.GenTraversableOnce)

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

Finds the first element of the collection or iterator 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 collection or iterator that satisfies p , or None if none exists.
  • Definition Classes
    • GenTraversableOnce

(defined at scala.collection.GenTraversableOnce)

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

Applies a binary operator to a start value and all elements of this collection 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 collection 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 collection or iterator. Returns
 `z` if this collection or iterator is empty.
  • Definition Classes
    • GenTraversableOnce

(defined at scala.collection.GenTraversableOnce)

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

Applies a binary operator to all elements of this collection or iterator 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 collection 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 collection or iterator. Returns
 `z` if this collection or iterator is empty.
  • Definition Classes
    • GenTraversableOnce

(defined at scala.collection.GenTraversableOnce)

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

Folds the elements of this collection 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 collection or iterator is empty.
  • Definition Classes
    • GenTraversableOnce

(defined at scala.collection.GenTraversableOnce)

abstract def forall(p: (A) ⇒ Boolean): Boolean

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

Note: may not terminate for infinite-sized collections.

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

(defined at scala.collection.GenTraversableOnce)

abstract def mkString(sep: String): String

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

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

Example:

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

(defined at scala.collection.GenTraversableOnce)

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

Displays all elements of this collection 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 collection 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 collection or iterator are separated by the string sep .
  • Definition Classes
    • GenTraversableOnce

Example:

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

(defined at scala.collection.GenTraversableOnce)

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

Optionally applies a binary operator to all elements of this collection 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 collection or iterator is nonempty, None otherwise.
  • Definition Classes
    • GenTraversableOnce

(defined at scala.collection.GenTraversableOnce)

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

Reduces the elements of this collection 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
    • GenTraversableOnce

(defined at scala.collection.GenTraversableOnce)

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

Optionally applies a binary operator to all elements of this collection 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 collection or iterator is nonempty, None otherwise.
  • Definition Classes
    • GenTraversableOnce

(defined at scala.collection.GenTraversableOnce)

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

Applies a binary operator to all elements of this collection 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
    • the result of inserting op between consecutive elements of this collection or iterator, going right to left:
    op(x_1, op(x_2, ..., op(x_{n-1}, x_n)...))
    
where `x1, ..., xn` are the elements of this collection or iterator.
  • Definition Classes
    • GenTraversableOnce
  • Exceptions thrown
    • UnsupportedOperationException if this collection or iterator is empty.

(defined at scala.collection.GenTraversableOnce)

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

Reduces the elements of this collection 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 collection or iterator is nonempty.
  • Definition Classes
    • GenTraversableOnce
  • Exceptions thrown
    • UnsupportedOperationException if this collection or iterator is empty.

(defined at scala.collection.GenTraversableOnce)

abstract def toBuffer[A1 >: A]: Buffer[A1]

Uses the contents of this collection or iterator to create a new mutable buffer.

Note: will not terminate for infinite-sized collections.

  • returns
    • a buffer containing all elements of this collection or iterator.
  • Definition Classes
    • GenTraversableOnce

(defined at scala.collection.GenTraversableOnce)

abstract def toIndexedSeq: immutable.IndexedSeq[A]

Converts this collection or iterator to an indexed sequence.

Note: will not terminate for infinite-sized collections.

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

(defined at scala.collection.GenTraversableOnce)

abstract def toIterable: GenIterable[A]

Converts this collection or iterator to an iterable collection. Note that the choice of target Iterable is lazy in this default implementation as this TraversableOnce may be lazy and unevaluated (i.e. it may be an iterator which is only traversable once).

Note: will not terminate for infinite-sized collections.

  • returns
    • an Iterable containing all elements of this collection or iterator.
  • Definition Classes
    • GenTraversableOnce

(defined at scala.collection.GenTraversableOnce)

abstract def toSeq: GenSeq[A]

Converts this collection or iterator to a sequence. As with toIterable , it’s lazy in this default implementation, as this TraversableOnce may be lazy and unevaluated.

Note: will not terminate for infinite-sized collections.

  • returns
    • a sequence containing all elements of this collection or iterator.
  • Definition Classes
    • GenTraversableOnce

(defined at scala.collection.GenTraversableOnce)

abstract def toSet[A1 >: A]: GenSet[A1]

Converts this collection or iterator to a set.

Note: will not terminate for infinite-sized collections.

  • returns
    • a set containing all elements of this collection or iterator.
  • Definition Classes
    • GenTraversableOnce

(defined at scala.collection.GenTraversableOnce)

abstract def toTraversable: GenTraversable[A]

Converts this collection or iterator 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 collection or iterator.
  • Definition Classes
    • GenTraversableOnce

(defined at scala.collection.GenTraversableOnce)

Concrete Value Members From scala.collection.GenTraversableOnce

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

[use case]

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

Note: will not terminate for infinite-sized collections.

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

(defined at scala.collection.GenTraversableOnce)

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

[use case]

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

Note: will not terminate for infinite-sized collections.

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

(defined at scala.collection.GenTraversableOnce)

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

[use case]

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

Note: will not terminate for infinite-sized collections.

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

(defined at scala.collection.GenTraversableOnce)

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

[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 general collection with the largest value measured by function f.
  • Definition Classes
    • GenTraversableOnce

(defined at scala.collection.GenTraversableOnce)

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

[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 general collection with the smallest value measured by function f.
  • Definition Classes
    • GenTraversableOnce

(defined at scala.collection.GenTraversableOnce)

abstract def toMap[K, V](implicit ev: <:<[A, (K, V)]): GenMap[K, V]

[use case]

Converts this general collection 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.

Note: will not terminate for infinite-sized collections.

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

(defined at scala.collection.GenTraversableOnce)

Abstract Value Members From scala.collection.Parallelizable

abstract def parCombiner: Combiner[A, ParIterable[A]]

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
    • Parallelizable

(defined at scala.collection.Parallelizable)

abstract def seq: TraversableOnce[A]

  • Definition Classes
    • Parallelizable

(defined at scala.collection.Parallelizable)

Concrete Value Members From scala.collection.Parallelizable

def par: ParIterable[A]

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 Implicit scala.collection.parallel.CollectionsHaveToParArray ——————————————————————————–

def toParArray: ParArray[T]

  • Implicit information
    • This member is added by an implicit conversion from GenTraversableLike [A, Repr] to CollectionsHaveToParArray [GenTraversableLike [A, Repr], T] performed by method CollectionsHaveToParArray in scala.collection.parallel. This conversion will take place only if an implicit value of type ( GenTraversableLike [A, Repr]) ⇒ 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 scala.annotation.migration


/** A template trait for all traversable collections upon which operations
 *  may be implemented in parallel.
 *
 *  @define thatinfo 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.
 *  @define bfinfo 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`.
 *  @define orderDependent
 *
 *    Note: might return different results for different runs, unless the
 *    underlying collection type is ordered.
 *  @define orderDependentFold
 *
 *    Note: might return different results for different runs, unless the
 *    underlying collection type is ordered.
 *    or the operator is associative and commutative.
 *  @define mayNotTerminateInf
 *
 *    Note: may not terminate for infinite-sized collections.
 *  @define willNotTerminateInf
 *
 *    Note: will not terminate for infinite-sized collections.
 *
 *  @define traversableInfo
 *  This is a base trait of all kinds of Scala collections.
 *
 *  @define Coll `GenTraversable`
 *  @define coll general collection
 *  @define collectExample
 *  @tparam A    the collection element type.
 *  @tparam Repr the actual type of the element container.
 *
 *  @author Martin Odersky
 *  @author Aleksandar Prokopec
 *  @since 2.9
 */
trait GenTraversableLike[+A, +Repr] extends Any with GenTraversableOnce[A] with Parallelizable[A, parallel.ParIterable[A]] {

  def repr: Repr

  def size: Int

  /** Selects the first element of this $coll.
   *  $orderDependent
   *  @return  the first element of this $coll.
   *  @throws NoSuchElementException if the $coll is empty.
   */
  def head: A

  /** Optionally selects the first element.
   *  $orderDependent
   *  @return  the first element of this $coll if it is nonempty,
   *           `None` if it is empty.
   */
  def headOption: Option[A]

  /** Tests whether this $coll can be repeatedly traversed.
   *  @return   `true`
   */
  def isTraversableAgain: Boolean

  /** Selects all elements except the first.
   *  $orderDependent
   *  @return  a $coll consisting of all elements of this $coll
   *           except the first one.
   *  @throws UnsupportedOperationException if the $coll is empty.
   */
  def tail: Repr

  /** Selects the last element.
    * $orderDependent
    * @return The last element of this $coll.
    * @throws NoSuchElementException If the $coll is empty.
    */
  def last: A

  /** Optionally selects the last element.
   *  $orderDependent
   *  @return  the last element of this $coll$ if it is nonempty,
   *           `None` if it is empty.
   */
  def lastOption: Option[A]

  /** Selects all elements except the last.
   *  $orderDependent
   *  @return  a $coll consisting of all elements of this $coll
   *           except the last one.
   *  @throws UnsupportedOperationException if the $coll is empty.
   */
  def init: Repr

  /** Computes a prefix scan of the elements of the collection.
   *
   *  Note: The neutral element `z` may be applied more than once.
   *
   *  @tparam B         element type of the resulting collection
   *  @tparam That      type of the resulting collection
   *  @param z          neutral element for the operator `op`
   *  @param op         the associative operator for the scan
   *  @param cbf        combiner factory which provides a combiner
   *
   *  @return           a new $coll containing the prefix scan of the elements in this $coll
   */
  def scan[B >: A, That](z: B)(op: (B, B) => B)(implicit cbf: CanBuildFrom[Repr, B, That]): That

  /** Produces a collection containing cumulative results of applying the
   *  operator going left to right.
   *
   *  $willNotTerminateInf
   *  $orderDependent
   *
   *  @tparam B      the type of the elements in the resulting collection
   *  @tparam That   the actual type of the resulting collection
   *  @param z       the initial value
   *  @param op      the binary operator applied to the intermediate result and the element
   *  @param bf      $bfinfo
   *  @return        collection with intermediate results
   */
  def scanLeft[B, That](z: B)(op: (B, A) => B)(implicit bf: CanBuildFrom[Repr, 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.
   *  $willNotTerminateInf
   *  $orderDependent
   *
   *  Example:
   *  {{{
   *    List(1, 2, 3, 4).scanRight(0)(_ + _) == List(10, 9, 7, 4, 0)
   *  }}}
   *
   *  @tparam B      the type of the elements in the resulting collection
   *  @tparam That   the actual type of the resulting collection
   *  @param z       the initial value
   *  @param op      the binary operator applied to the intermediate result and the element
   *  @param bf      $bfinfo
   *  @return        collection with intermediate results
   */
  @migration("The behavior of `scanRight` has changed. The previous behavior can be reproduced with scanRight.reverse.", "2.9.0")
  def scanRight[B, That](z: B)(op: (A, B) => B)(implicit bf: CanBuildFrom[Repr, B, That]): That

  def foreach[U](f: A => U): Unit

  /** Builds a new collection by applying a function to all elements of this $coll.
   *
   *  @param f      the function to apply to each element.
   *  @tparam B     the element type of the returned collection.
   *  @tparam That  $thatinfo
   *  @param bf     $bfinfo
   *  @return       a new collection of type `That` resulting from applying the given function
   *                `f` to each element of this $coll and collecting the results.
   *
   *  @usecase def map[B](f: A => B): $Coll[B]
   *    @inheritdoc
   *    @return       a new $coll resulting from applying the given function
   *                  `f` to each element of this $coll and collecting the results.
   */
  def map[B, That](f: A => B)(implicit bf: CanBuildFrom[Repr, B, That]): That

  /** Builds a new collection by applying a partial function to all elements of this $coll
   *  on which the function is defined.
   *
   *  @param pf     the partial function which filters and maps the $coll.
   *  @tparam B     the element type of the returned collection.
   *  @tparam That  $thatinfo
   *  @param bf     $bfinfo
   *  @return       a new collection of type `That` resulting from applying the partial function
   *                `pf` to each element on which it is defined and collecting the results.
   *                The order of the elements is preserved.
   *
   *  @usecase def collect[B](pf: PartialFunction[A, B]): $Coll[B]
   *    @inheritdoc
   *
   *    $collectExample
   *
   *    @return       a new $coll 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.
   */
  def collect[B, That](pf: PartialFunction[A, B])(implicit bf: CanBuildFrom[Repr, B, That]): That

  /** Builds a new collection by applying a function to all elements of this $coll
   *  and using the elements of the resulting collections.
   *
   *  @param f      the function to apply to each element.
   *  @tparam B     the element type of the returned collection.
   *  @tparam That  $thatinfo
   *  @param bf     $bfinfo
   *  @return       a new collection of type `That` resulting from applying the given collection-valued function
   *                `f` to each element of this $coll and concatenating the results.
   *
   *  @usecase def flatMap[B](f: A => GenTraversableOnce[B]): $Coll[B]
   *    @inheritdoc
   *
   *    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 $coll. 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)
   *    }}}
   *
   *    @return       a new $coll resulting from applying the given collection-valued function
   *                  `f` to each element of this $coll and concatenating the results.
   */
  def flatMap[B, That](f: A => GenTraversableOnce[B])(implicit bf: CanBuildFrom[Repr, B, That]): That

  /** Returns a new $coll containing the elements from the left hand operand followed by the elements from the
   *  right hand operand. The element type of the $coll is the most specific superclass encompassing
   *  the element types of the two operands.
   *
   *  @param that   the traversable to append.
   *  @tparam B     the element type of the returned collection.
   *  @tparam That  $thatinfo
   *  @param bf     $bfinfo
   *  @return       a new collection of type `That` which contains all elements
   *                of this $coll followed by all elements of `that`.
   *
   *  @usecase def ++[B](that: GenTraversableOnce[B]): $Coll[B]
   *    @inheritdoc
   *
   *    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)
   *    }}}
   *
   *    @return       a new $coll which contains all elements of this $coll
   *                  followed by all elements of `that`.
   */
  def ++[B >: A, That](that: GenTraversableOnce[B])(implicit bf: CanBuildFrom[Repr, B, That]): That

  /** Selects all elements of this $coll which satisfy a predicate.
   *
   *  @param pred  the predicate used to test elements.
   *  @return      a new $coll consisting of all elements of this $coll that satisfy the given
   *               predicate `p`. Their order may not be preserved.
   */
  def filter(pred: A => Boolean): Repr

  /** Selects all elements of this $coll which do not satisfy a predicate.
   *
   *  @param pred  the predicate used to test elements.
   *  @return      a new $coll consisting of all elements of this $coll that do not satisfy the given
   *               predicate `p`. Their order may not be preserved.
   */
  def filterNot(pred: A => Boolean): Repr

  /** Partitions this $coll in two ${coll}s according to a predicate.
   *
   *  @param pred the predicate on which to partition.
   *  @return     a pair of ${coll}s: the first $coll consists of all elements that
   *              satisfy the predicate `p` and the second $coll consists of all elements
   *              that don't. The relative order of the elements in the resulting ${coll}s
   *              may not be preserved.
   */
  def partition(pred: A => Boolean): (Repr, Repr)

  /** Partitions this $coll into a map of ${coll}s 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 $coll.
   *
   *  @param f     the discriminator function.
   *  @tparam K    the type of keys returned by the discriminator function.
   *  @return      A map from keys to ${coll}s 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 $coll of those elements `x`
   *               for which `f(x)` equals `k`.
   *
   */
  def groupBy[K](f: A => K): GenMap[K, Repr]

  /** Selects first ''n'' elements.
   *  $orderDependent
   *  @param  n    the number of elements to take from this $coll.
   *  @return a $coll consisting only of the first `n` elements of this $coll,
   *          or else the whole $coll, if it has less than `n` elements.
   */
  def take(n: Int): Repr

  /** Selects all elements except first ''n'' ones.
   *  $orderDependent
   *  @param  n    the number of elements to drop from this $coll.
   *  @return a $coll consisting of all elements of this $coll except the first `n` ones, or else the
   *          empty $coll, if this $coll has less than `n` elements.
   */
  def drop(n: Int): Repr

  /** Selects an interval of elements.  The returned collection is made up
   *  of all elements `x` which satisfy the invariant:
   *  {{{
   *    from <= indexOf(x) < until
   *  }}}
   *  $orderDependent
   *
   *  @param unc_from   the lowest index to include from this $coll.
   *  @param unc_until  the lowest index to EXCLUDE from this $coll.
   *  @return  a $coll containing the elements greater than or equal to
   *           index `from` extending up to (but not including) index `until`
   *           of this $coll.
   */
  def slice(unc_from: Int, unc_until: Int): Repr

  /** Splits this $coll into two at a given position.
   *  Note: `c splitAt n` is equivalent to (but possibly more efficient than)
   *         `(c take n, c drop n)`.
   *  $orderDependent
   *
   *  @param n the position at which to split.
   *  @return  a pair of ${coll}s consisting of the first `n`
   *           elements of this $coll, and the other elements.
   */
  def splitAt(n: Int): (Repr, Repr)

  /** Takes longest prefix of elements that satisfy a predicate.
   *  $orderDependent
   *  @param   pred  The predicate used to test elements.
   *  @return  the longest prefix of this $coll whose elements all satisfy
   *           the predicate `p`.
   */
  def takeWhile(pred: A => Boolean): Repr

  /** Splits this $coll 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.
   *  $orderDependent
   *
   *  @param pred the test predicate
   *  @return  a pair consisting of the longest prefix of this $coll whose
   *           elements all satisfy `p`, and the rest of this $coll.
   */
  def span(pred: A => Boolean): (Repr, Repr)

  /** Drops longest prefix of elements that satisfy a predicate.
   *  $orderDependent
   *  @param   pred  The predicate used to test elements.
   *  @return  the longest suffix of this $coll whose first element
   *           does not satisfy the predicate `p`.
   */
  def dropWhile(pred: A => Boolean): Repr

  /** Defines the prefix of this object's `toString` representation.
   *
   *  @return  a string representation which starts the result of `toString`
   *           applied to this $coll. By default the string prefix is the
   *           simple name of the collection class $coll.
   */
  def stringPrefix: String

}