ParIterable
Related Docs:
object ParIterable
| package parallel
Standard accessor task that iterates over the elements of the collection.
Standard accessor task that iterates over the elements of the collection.
type of the result of this method (R for result).
the representation type of the task at hand.
Performs two tasks in parallel, and waits for both to finish.
Performs two tasks in parallel, and waits for both to finish.
Sequentially performs one task after another.
Sequentially performs one task after another.
The size of this general collection.
The size of this general collection.
Note: will not terminate for infinite-sized collections.
the number of elements in this general collection.
Creates a new parallel iterator used to traverse the elements of this parallel collection.
Creates a new parallel iterator used to traverse the elements of this parallel collection.
This iterator is more specific than the iterator of the returned by iterator, and augmented
with additional accessor and transformer methods.
a parallel iterator
Test two objects for inequality.
Test two objects for inequality.
true if !(this == that), false otherwise.
Equivalent to x.hashCode except for boxed numeric types and null.
Equivalent to x.hashCode except for boxed numeric types and null.
For numerics, it returns a hash value which is consistent
with value equality: if two value type instances compare
as true, then ## will produce the same hash value for each
of them.
For null returns a hashcode where null.hashCode throws a
NullPointerException.
a hash value consistent with ==
[use case] Returns a new parallel iterable containing the elements from the left hand operand followed by the elements from the right hand operand.
Returns a new parallel iterable containing the elements from the left hand operand followed by the elements from the right hand operand. The element type of the parallel iterable 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)
the element type of the returned collection.
the traversable to append.
a new parallel iterable which contains all elements of this parallel iterable
followed by all elements of that.
Applies a binary operator to a start value and all elements of this parallel iterable, going left to right.
Applies a binary operator to a start value and all elements of this parallel iterable, 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.
the start value.
the binary operator.
the result of inserting op between consecutive elements of this parallel iterable,
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 parallel iterable.
Applies a binary operator to all elements of this parallel iterable and a start value, going right to left.
Applies a binary operator to all elements of this parallel iterable 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
the start value
the binary operator
the result of inserting op between consecutive elements of this parallel iterable,
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 parallel iterable.
The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).
The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).
the object to compare against this object for equality.
true if the receiver object is equivalent to the argument; false otherwise.
Aggregates the results of applying an operator to subsequent elements.
Aggregates the results of applying an operator to subsequent elements.
This is a more general form of fold and reduce. It has similar semantics, but does
not require the result to be a supertype of the element type. It traverses the elements in
different partitions sequentially, using seqop to update the result, and then
applies combop to results from different partitions. The implementation of this
operation may operate on an arbitrary number of collection partitions, so combop
may be invoked arbitrary number of times.
For example, one might want to process some elements and then produce a Set. In this
case, seqop would process an element and append it to the set, while combop
would concatenate two sets from different partitions together. The initial value
z would be an empty set.
pc.aggregate(Set[Int]())(_ += process(_), _ ++ _)
Another example is calculating geometric mean from a collection of doubles (one would typically require big doubles for this).
the type of accumulated results
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
an operator used to accumulate results within a partition
an associative operator used to combine results from different partitions
Cast the receiver object to be of type T0.
Cast the receiver object to be of type T0.
Note that the success of a cast at runtime is modulo Scala's erasure semantics.
Therefore the expression 1.asInstanceOf[String] will throw a ClassCastException at
runtime, while the expression List(1).asInstanceOf[List[String]] will not.
In the latter example, because the type argument is erased as part of compilation it is
not possible to check whether the contents of the list are of the requested type.
the receiver object.
ClassCastException if the receiver object is not an instance of the erasure of type T0.
Create a copy of the receiver object.
[use case] Builds a new collection by applying a partial function to all elements of this parallel iterable on which the function is defined.
Builds a new collection by applying a partial function to all elements of this parallel iterable on which the function is defined.
the element type of the returned collection.
the partial function which filters and maps the parallel iterable.
a new parallel iterable 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.
Creates a combiner factory.
Creates a combiner factory. Each combiner factory instance is used once per invocation of a parallel transformer method for a single collection.
The default combiner factory creates a new combiner every time it
is requested, unless the combiner is thread-safe as indicated by its
canBeShared method. In this case, the method returns a factory which
returns the same combiner each time. This is typically done for
concurrent parallel collections, the combiners of which allow
thread safe access.
The factory companion object that builds instances of class ParIterable.
The factory companion object that builds instances of class ParIterable.
(or its Iterable superclass where class ParIterable is not a Seq.)
[use case] Copies values of this parallel iterable to an array.
Copies values of this parallel iterable to an array.
Fills the given array xs with values of this parallel iterable, beginning at index start.
Copying will stop once either the end of the current parallel iterable is reached,
or the end of the array is reached.
Note: will not terminate for infinite-sized collections.
the array to fill.
the starting index.
[use case] Copies values of this parallel iterable to an array.
Copies values of this parallel iterable to an array.
Fills the given array xs with values of this parallel iterable.
Copying will stop once either the end of the current parallel iterable is reached,
or the end of the array is reached.
Note: will not terminate for infinite-sized collections.
the array to fill.
Counts the number of elements in the parallel iterable which satisfy a predicate.
Counts the number of elements in the parallel iterable which satisfy a predicate.
the predicate used to test elements.
the number of elements satisfying the predicate p.
Selects all elements except first n ones.
Selects all elements except first n ones.
Note: might return different results for different runs, unless the underlying collection type is ordered.
the number of elements to drop from this parallel iterable.
a parallel iterable consisting of all elements of this parallel iterable except the first n ones, or else the
empty parallel iterable, if this parallel iterable has less than n elements.
Drops all elements in the longest prefix of elements that satisfy the predicate, and returns a collection composed of the remaining elements.
Drops all elements in the longest prefix of elements that satisfy the predicate, and returns a collection composed of the remaining elements.
This method will use indexFlag signalling capabilities. This means
that splitters may set and read the indexFlag state.
The index flag is initially set to maximum integer value.
the predicate used to test the elements
a collection composed of all the elements after the longest prefix of elements
in this parallel iterable that satisfy the predicate pred
Tests whether the argument (arg0) is a reference to the receiver object (this).
Tests whether the argument (arg0) is a reference to the receiver object (this).
The eq method implements an equivalence relation on
non-null instances of AnyRef, and has three additional properties:
x and y of type AnyRef, multiple invocations of
x.eq(y) consistently returns true or consistently returns false.x of type AnyRef, x.eq(null) and null.eq(x) returns false.null.eq(null) returns true. When overriding the equals or hashCode methods, it is important to ensure that their behavior is
consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2), they
should be equal to each other (o1 == o2) and they should hash to the same value (o1.hashCode == o2.hashCode).
true if the argument is a reference to the receiver object; false otherwise.
The equality method for reference types.
Tests whether a predicate holds for some element of this parallel iterable.
Tests whether a predicate holds for some element of this parallel iterable.
This method will use abort signalling capabilities. This means
that splitters may send and read abort signals.
a predicate used to test elements
true if p holds for some element, false otherwise
Selects all elements of this parallel iterable which satisfy a predicate.
Selects all elements of this parallel iterable which satisfy a predicate.
the predicate used to test elements.
a new parallel iterable consisting of all elements of this parallel iterable that satisfy the given
predicate p. Their order may not be preserved.
Selects all elements of this parallel iterable which do not satisfy a predicate.
Selects all elements of this parallel iterable which do not satisfy a predicate.
the predicate used to test elements.
a new parallel iterable consisting of all elements of this parallel iterable that do not satisfy the given
predicate p. Their order may not be preserved.
Called by the garbage collector on the receiver object when there are no more references to the object.
Called by the garbage collector on the receiver object when there are no more references to the object.
The details of when and if the finalize method is invoked, as
well as the interaction between finalize and non-local returns
and exceptions, are all platform dependent.
Finds some element in the collection for which the predicate holds, if such an element exists.
Finds some element in the collection for which the predicate holds, if such an element exists. The element may not necessarily be the first such element in the iteration order.
If there are multiple elements obeying the predicate, the choice is nondeterministic.
This method will use abort signalling capabilities. This means
that splitters may send and read abort signals.
predicate used to test the elements
an option value with the element if such an element exists, or None otherwise
[use case] Builds a new collection by applying a function to all elements of this parallel iterable and using the elements of the resulting collections.
Builds a new collection by applying a function to all elements of this parallel iterable 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 parallel iterable. 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)
the element type of the returned collection.
the function to apply to each element.
a new parallel iterable resulting from applying the given collection-valued function
f to each element of this parallel iterable and concatenating the results.
[use case] Converts this parallel iterable of traversable collections into a parallel iterable formed by the elements of these traversable collections.
Converts this parallel iterable of traversable collections into a parallel iterable formed by the elements of these traversable collections.
The resulting collection's type will be guided by the static type of parallel iterable. For example:
val xs = List( Set(1, 2, 3), Set(1, 2, 3) ).flatten // xs == List(1, 2, 3, 1, 2, 3) val ys = Set( List(1, 2, 3), List(3, 2, 1) ).flatten // ys == Set(1, 2, 3)
the type of the elements of each traversable collection.
a new parallel iterable resulting from concatenating all element parallel iterables.
Folds the elements of this sequence using the specified associative binary operator.
Folds the elements of this sequence using the specified associative binary operator. The order in which the elements are reduced is unspecified and may be nondeterministic.
Note this method has a different signature than the foldLeft
and foldRight methods of the trait Traversable.
The result of folding may only be a supertype of this parallel collection's
type parameter T.
a type parameter for the binary operator, a supertype of T.
a neutral element for the fold operation, it may be added to the result
an arbitrary number of times, not changing the result (e.g. Nil for list concatenation,
0 for addition, or 1 for multiplication)
a binary operator that must be associative
the result of applying fold operator op between all the elements and z
Applies a binary operator to a start value and all elements of this parallel iterable, going left to right.
Applies a binary operator to a start value and all elements of this parallel iterable, 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.
the start value.
the binary operator.
the result of inserting op between consecutive elements of this parallel iterable,
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 parallel iterable.
Applies a binary operator to all elements of this parallel iterable and a start value, going right to left.
Applies a binary operator to all elements of this parallel iterable 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.
the start value.
the binary operator.
the result of inserting op between consecutive elements of this parallel iterable,
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 parallel iterable.
Tests whether a predicate holds for all elements of this parallel iterable.
Tests whether a predicate holds for all elements of this parallel iterable.
This method will use abort signalling capabilities. This means
that splitters may send and read abort signals.
a predicate used to test elements
true if p holds for all elements, false otherwise
Applies a function f to all the elements of parallel iterable in an undefined order.
Applies a function f to all the elements of parallel iterable in an undefined order.
the result type of the function applied to each element, which is always discarded
function applied to each element
Returns string formatted according to given format string.
Returns string formatted according to given format string.
Format strings are as for String.format
(@see java.lang.String.format).
The generic builder that builds instances of Traversable at arbitrary element types.
The generic builder that builds instances of Traversable at arbitrary element types.
A representation that corresponds to the dynamic class of the receiver object.
A representation that corresponds to the dynamic class of the receiver object.
The nature of the representation is platform dependent.
a representation that corresponds to the dynamic class of the receiver object.
not specified by SLS as a member of AnyRef
Partitions this parallel iterable into a map of parallel iterables according to some discriminator function.
Partitions this parallel iterable into a map of parallel iterables 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 parallel iterable.
the type of keys returned by the discriminator function.
the discriminator function.
A map from keys to parallel iterables 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 parallel iterable of those elements x
for which f(x) equals k.
The hashCode method for reference types.
Selects the first element of this parallel iterable.
Selects the first element of this parallel iterable.
Note: might return different results for different runs, unless the underlying collection type is ordered.
the first element of this parallel iterable.
NoSuchElementException if the parallel iterable is empty.
Optionally selects the first element.
Optionally selects the first element.
Note: might return different results for different runs, unless the underlying collection type is ordered.
the first element of this parallel iterable if it is nonempty,
None if it is empty.
Selects all elements except the last.
Selects all elements except the last.
Note: might return different results for different runs, unless the underlying collection type is ordered.
a parallel iterable consisting of all elements of this parallel iterable except the last one.
UnsupportedOperationException if the parallel iterable is empty.
Tests whether the parallel iterable is empty.
Tests whether the parallel iterable is empty.
true if the parallel iterable contains no elements, false otherwise.
Test whether the dynamic type of the receiver object is T0.
Test whether the dynamic type of the receiver object is T0.
Note that the result of the test is modulo Scala's erasure semantics.
Therefore the expression 1.isInstanceOf[String] will return false, while the
expression List(1).isInstanceOf[List[String]] will return true.
In the latter example, because the type argument is erased as part of compilation it is
not possible to check whether the contents of the list are of the specified type.
true if the receiver object is an instance of erasure of type T0; false otherwise.
Denotes whether this parallel collection has strict splitters.
Denotes whether this parallel collection has strict splitters.
This is true in general, and specific collection instances may choose to
override this method. Such collections will fail to execute methods
which rely on splitters being strict, i.e. returning a correct value
in the remaining method.
This method helps ensure that such failures occur on method invocations, rather than later on and in unpredictable ways.
Tests whether this parallel iterable can be repeatedly traversed.
Tests whether this parallel iterable can be repeatedly traversed.
true
Creates a new split iterator used to traverse the elements of this collection.
Creates a new split iterator used to traverse the elements of this collection.
By default, this method is implemented in terms of the protected splitter method.
a split iterator
Selects the last element.
Selects the last element.
Note: might return different results for different runs, unless the underlying collection type is ordered.
The last element of this parallel iterable.
NoSuchElementException If the parallel iterable is empty.
Optionally selects the last element.
Optionally selects the last element.
Note: might return different results for different runs, unless the underlying collection type is ordered.
the last element of this parallel iterable$ if it is nonempty,
None if it is empty.
[use case] Builds a new collection by applying a function to all elements of this parallel iterable.
Builds a new collection by applying a function to all elements of this parallel iterable.
the element type of the returned collection.
the function to apply to each element.
a new parallel iterable resulting from applying the given function
f to each element of this parallel iterable and collecting the results.
[use case] Finds the largest element.
Finds the largest element.
the largest element of this parallel iterable.
[use case] Finds the first element which yields the largest value measured by function f.
Finds the first element which yields the largest value measured by function f.
The result type of the function f.
The measuring function.
the first element of this parallel iterable with the largest value measured by function f.
[use case] Finds the smallest element.
Finds the smallest element.
the smallest element of this parallel iterable
[use case] Finds the first element which yields the smallest value measured by function f.
Finds the first element which yields the smallest value measured by function f.
The result type of the function f.
The measuring function.
the first element of this parallel iterable with the smallest value measured by function f.
Displays all elements of this parallel iterable in a string.
Displays all elements of this parallel iterable in a string.
a string representation of this parallel iterable. In the resulting string
the string representations (w.r.t. the method toString)
of all elements of this parallel iterable follow each other without any
separator string.
Displays all elements of this parallel iterable in a string using a separator string.
Displays all elements of this parallel iterable in a string using a separator string.
the separator string.
a string representation of this parallel iterable. In the resulting string
the string representations (w.r.t. the method toString)
of all elements of this parallel iterable are separated by the string sep.
List(1, 2, 3).mkString("|") = "1|2|3"
Displays all elements of this parallel iterable in a string using start, end, and separator strings.
Displays all elements of this parallel iterable in a string using start, end, and separator strings.
the starting string.
the separator string.
the ending string.
a string representation of this parallel iterable. 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 parallel iterable are separated by
the string sep.
List(1, 2, 3).mkString("(", "; ", ")") = "(1; 2; 3)"
Equivalent to !(this eq that).
Equivalent to !(this eq that).
true if the argument is not a reference to the receiver object; false otherwise.
The builder that builds instances of type Traversable[A]
The builder that builds instances of type Traversable[A]
Tests whether the parallel iterable is not empty.
Tests whether the parallel iterable is not empty.
true if the parallel iterable contains at least one element, false otherwise.
Wakes up a single thread that is waiting on the receiver object's monitor.
Wakes up a single thread that is waiting on the receiver object's monitor.
not specified by SLS as a member of AnyRef
Wakes up all threads that are waiting on the receiver object's monitor.
Wakes up all threads that are waiting on the receiver object's monitor.
not specified by SLS as a member of AnyRef
Returns a parallel implementation of this collection.
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.
a parallel implementation of this collection
The default par implementation uses the combiner provided by this method
to create a new parallel collection.
The default par implementation uses the combiner provided by this method
to create a new parallel collection.
a combiner for the parallel collection of type ParRepr
Partitions this parallel iterable in two parallel iterables according to a predicate.
Partitions this parallel iterable in two parallel iterables according to a predicate.
the predicate on which to partition.
a pair of parallel iterables: the first parallel iterable consists of all elements that
satisfy the predicate p and the second parallel iterable consists of all elements
that don't. The relative order of the elements in the resulting parallel iterables
may not be preserved.
[use case] Multiplies up the elements of this collection.
Multiplies up the elements of this collection.
the product of all elements in this parallel iterable of numbers of type Int.
Instead of Int, any other type T with an implicit Numeric[T] implementation
can be used as element type of the parallel iterable and as result type of product.
Examples of such types are: Long, Float, Double, BigInt.
Reduces the elements of this sequence using the specified associative binary operator.
Reduces the elements of this sequence using the specified associative binary operator.
The order in which operations are performed on elements is unspecified and may be nondeterministic.
Note this method has a different signature than the reduceLeft
and reduceRight methods of the trait Traversable.
The result of reducing may only be a supertype of this parallel collection's
type parameter T.
A type parameter for the binary operator, a supertype of T.
A binary operator that must be associative.
The result of applying reduce operator op between all the elements if the collection is nonempty.
UnsupportedOperationException
if this parallel iterable is empty.
Optionally applies a binary operator to all elements of this parallel iterable, going left to right.
Optionally applies a binary operator to all elements of this parallel iterable, 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.
the binary operator.
an option value containing the result of reduceLeft(op) if this parallel iterable is nonempty,
None otherwise.
Optionally reduces the elements of this sequence using the specified associative binary operator.
Optionally reduces the elements of this sequence using the specified associative binary operator.
The order in which operations are performed on elements is unspecified and may be nondeterministic.
Note this method has a different signature than the reduceLeftOption
and reduceRightOption methods of the trait Traversable.
The result of reducing may only be a supertype of this parallel collection's
type parameter T.
A type parameter for the binary operator, a supertype of T.
A binary operator that must be associative.
An option value containing result of applying reduce operator op between all
the elements if the collection is nonempty, and None otherwise.
Applies a binary operator to all elements of this parallel iterable, going right to left.
Applies a binary operator to all elements of this parallel iterable, 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.
the binary operator.
the result of inserting op between consecutive elements of this parallel iterable,
going right to left:
op(x_1, op(x_2, ..., op(x_{n-1}, x_n)...)) where x1, ..., xn are the elements of this parallel iterable.
UnsupportedOperationException if this parallel iterable is empty.
Optionally applies a binary operator to all elements of this parallel iterable, going right to left.
Optionally applies a binary operator to all elements of this parallel iterable, 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.
the binary operator.
an option value containing the result of reduceRight(op) if this parallel iterable is nonempty,
None otherwise.
Optionally reuses an existing combiner for better performance.
Optionally reuses an existing combiner for better performance. By default it doesn't - subclasses may override this behaviour.
The provided combiner oldc that can potentially be reused will be either some combiner from the previous computational task, or None if there
was no previous phase (in which case this method must return newc).
The combiner that is the result of the previous task, or None if there was no previous task.
The new, empty combiner that can be used.
Either newc or oldc.
[use case] Checks if the other iterable collection contains the same elements in the same order as this parallel iterable.
Checks if the other iterable collection contains the same elements in the same order as this parallel iterable.
Note: might return different results for different runs, unless the underlying collection type is ordered.
Note: will not terminate for infinite-sized collections.
the collection to compare with.
true, if both collections contain the same elements in the same order, false otherwise.
[use case] Computes a prefix scan of the elements of the collection.
Computes a prefix scan of the elements of the collection.
Note: The neutral element z may be applied more than once.
neutral element for the operator op
the associative operator for the scan
a new parallel iterable containing the prefix scan of the elements in this parallel iterable
Produces a collection containing cumulative results of applying the operator going left to right.
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.
the actual type of the resulting collection
the initial value
the binary operator applied to the intermediate result and the element
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.
collection with intermediate results
Produces a collection containing cumulative results of applying the operator going right to left.
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)
the actual type of the resulting collection
the initial value
the binary operator applied to the intermediate result and the element
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.
collection with intermediate results
Selects an interval of elements.
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.
the lowest index to include from this parallel iterable.
the lowest index to EXCLUDE from this parallel iterable.
a parallel iterable containing the elements greater than or equal to
index from extending up to (but not including) index until
of this parallel iterable.
Splits this parallel iterable into a prefix/suffix pair according to a predicate.
Splits this parallel iterable into a prefix/suffix pair according to a predicate.
This method will use indexFlag signalling capabilities. This means
that splitters may set and read the indexFlag state.
The index flag is initially set to maximum integer value.
the predicate used to test the elements
a pair consisting of the longest prefix of the collection for which all
the elements satisfy pred, and the rest of the collection
Splits this parallel iterable into two at a given position.
Splits this parallel iterable 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.
the position at which to split.
a pair of parallel iterables consisting of the first n
elements of this parallel iterable, and the other elements.
Defines the prefix of this object's toString representation.
Defines the prefix of this object's toString representation.
a string representation which starts the result of toString
applied to this parallel iterable. By default the string prefix is the
simple name of the collection class parallel iterable.
[use case] Sums up the elements of this collection.
Sums up the elements of this collection.
the sum of all elements in this parallel iterable of numbers of type Int.
Instead of Int, any other type T with an implicit Numeric[T] implementation
can be used as element type of the parallel iterable and as result type of sum.
Examples of such types are: Long, Float, Double, BigInt.
Selects all elements except the first.
Selects all elements except the first.
Note: might return different results for different runs, unless the underlying collection type is ordered.
a parallel iterable consisting of all elements of this parallel iterable except the first one.
UnsupportedOperationException if the parallel iterable is empty.
Selects first n elements.
Selects first n elements.
Note: might return different results for different runs, unless the underlying collection type is ordered.
the number of elements to take from this parallel iterable.
a parallel iterable consisting only of the first n elements of this parallel iterable,
or else the whole parallel iterable, if it has less than n elements.
Takes the longest prefix of elements that satisfy the predicate.
Takes the longest prefix of elements that satisfy the predicate.
This method will use indexFlag signalling capabilities. This means
that splitters may set and read the indexFlag state.
The index flag is initially set to maximum integer value.
the predicate used to test the elements
the longest prefix of this parallel iterable of elements that satisfy the predicate pred
The task support object which is responsible for scheduling and load-balancing tasks to processors.
The task support object which is responsible for scheduling and load-balancing tasks to processors.
Changes the task support object which is responsible for scheduling and load-balancing tasks to processors.
Changes the task support object which is responsible for scheduling and load-balancing tasks to processors.
A task support object can be changed in a parallel collection after it has been created, but only during a quiescent period, i.e. while there are no concurrent invocations to parallel collection methods.
Here is a way to change the task support of a parallel collection:
import scala.collection.parallel._ val pc = mutable.ParArray(1, 2, 3) pc.tasksupport = new ForkJoinTaskSupport( new scala.concurrent.forkjoin.ForkJoinPool(2))
[use case] Converts this parallel iterable into another by copying all elements.
Converts this parallel iterable into another by copying all elements.
Note: will not terminate for infinite-sized collections.
The collection type to build.
a new collection containing all elements of this parallel iterable.
[use case] Converts this parallel iterable to an array.
Converts this parallel iterable to an array.
Note: will not terminate for infinite-sized collections.
an array containing all elements of this parallel iterable.
An ClassTag must be available for the element type of this parallel iterable.
Uses the contents of this parallel iterable to create a new mutable buffer.
Uses the contents of this parallel iterable to create a new mutable buffer.
Note: will not terminate for infinite-sized collections.
a buffer containing all elements of this parallel iterable.
Converts this parallel iterable to an indexed sequence.
Converts this parallel iterable to an indexed sequence.
Note: will not terminate for infinite-sized collections.
an indexed sequence containing all elements of this parallel iterable.
Converts this parallel iterable to an iterable collection.
Converts this parallel iterable 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.
an Iterable containing all elements of this parallel iterable.
Returns an Iterator over the elements in this parallel iterable.
Returns an Iterator over the elements in this parallel iterable. Will return the same Iterator if this instance is already an Iterator.
Note: will not terminate for infinite-sized collections.
an Iterator containing all elements of this parallel iterable.
Converts this parallel iterable to a list.
Converts this parallel iterable to a list.
Note: will not terminate for infinite-sized collections.
a list containing all elements of this parallel iterable.
[use case] Converts this parallel iterable to a map.
Converts this parallel iterable 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.
a map of type immutable.Map[T, U]
containing all key/value pairs of type (T, U) of this parallel iterable.
Converts this parallel iterable to a sequence.
Converts this parallel iterable 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.
a sequence containing all elements of this parallel iterable.
Converts this parallel iterable to a set.
Converts this parallel iterable to a set.
Note: will not terminate for infinite-sized collections.
a set containing all elements of this parallel iterable.
Converts this parallel iterable to a stream.
Converts this parallel iterable to a stream.
a stream containing all elements of this parallel iterable.
Creates a String representation of this object.
Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.
a String representation of the object.
Converts this parallel iterable to an unspecified Traversable.
Converts this parallel iterable to an unspecified Traversable. Will return the same collection if this instance is already Traversable.
Note: will not terminate for infinite-sized collections.
a Traversable containing all elements of this parallel iterable.
Converts this parallel iterable to a Vector.
Converts this parallel iterable to a Vector.
Note: will not terminate for infinite-sized collections.
a vector containing all elements of this parallel iterable.
Transposes this collection of traversable collections into a collection of collections.
Transposes this collection of traversable collections into a collection of collections.
The resulting collection's type will be guided by the static type of collection. For example:
val xs = List( Set(1, 2, 3), Set(4, 5, 6)).transpose // xs == List( // List(1, 4), // List(2, 5), // List(3, 6)) val ys = Vector( List(1, 2, 3), List(4, 5, 6)).transpose // ys == Vector( // Vector(1, 4), // Vector(2, 5), // Vector(3, 6))
the type of the elements of each traversable collection.
an implicit conversion which asserts that the
element type of this collection is a Traversable.
a two-dimensional collection of collections which has as nth row the nth column of this collection.
(Changed in version 2.9.0) transpose throws an IllegalArgumentException if collections are not uniformly sized.
IllegalArgumentException if all collections in this collection
are not of the same size.
Converts this collection of pairs into two collections of the first and second half of each pair.
Converts this collection of pairs into two collections of the first and second half of each pair.
val xs = Traversable( (1, "one"), (2, "two"), (3, "three")).unzip // xs == (Traversable(1, 2, 3), // Traversable(one, two, three))
the type of the first half of the element pairs
the type of the second half of the element pairs
an implicit conversion which asserts that the element type of this collection is a pair.
a pair of collections, containing the first, respectively second half of each element pair of this collection.
Converts this collection of triples into three collections of the first, second, and third element of each triple.
Converts this collection of triples into three collections of the first, second, and third element of each triple.
val xs = Traversable( (1, "one", '1'), (2, "two", '2'), (3, "three", '3')).unzip3 // xs == (Traversable(1, 2, 3), // Traversable(one, two, three), // Traversable(1, 2, 3))
the type of the first member of the element triples
the type of the second member of the element triples
the type of the third member of the element triples
an implicit conversion which asserts that the element type of this collection is a triple.
a triple of collections, containing the first, second, respectively third member of each element triple of this collection.
[use case] Returns a parallel iterable formed from this parallel iterable and another iterable collection by combining corresponding elements in pairs.
Returns a parallel iterable formed from this parallel iterable 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.
the type of the second half of the returned pairs
The iterable providing the second half of each result pair
a new parallel iterable containing pairs consisting of
corresponding elements of this parallel iterable and that. The length
of the returned collection is the minimum of the lengths of this parallel iterable and that.
[use case] Returns a parallel iterable formed from this parallel iterable and another iterable collection by combining corresponding elements in pairs.
Returns a parallel iterable formed from this parallel iterable 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.
the type of the second half of the returned pairs
The iterable providing the second half of each result pair
the element to be used to fill up the result if this parallel iterable is shorter than that.
the element to be used to fill up the result if that is shorter than this parallel iterable.
a new parallel iterable containing pairs consisting of
corresponding elements of this parallel iterable and that. The length
of the returned collection is the maximum of the lengths of this parallel iterable and that.
If this parallel iterable is shorter than that, thisElem values are used to pad the result.
If that is shorter than this parallel iterable, thatElem values are used to pad the result.
[use case] Zips this parallel iterable with its indices.
Zips this parallel iterable with its indices.
Note: might return different results for different runs, unless the underlying collection type is ordered.
A new parallel iterable containing pairs consisting of all elements of this
parallel iterable paired with their index. Indices start at 0.
List("a", "b", "c").zipWithIndex = List(("a", 0), ("b", 1), ("c", 2))
(Since version 2.11.0) Use .seq.view instead
A template trait for parallel iterable collections.
This is a base trait for Scala parallel collections. It defines behaviour common to all parallel collections. Concrete parallel collections should inherit this trait and
ParIterableif they want to define specific combiner factories.Parallel operations are implemented with divide and conquer style algorithms that parallelize well. The basic idea is to split the collection into smaller parts until they are small enough to be operated on sequentially.
All of the parallel operations are implemented as tasks within this trait. Tasks rely on the concept of splitters, which extend iterators. Every parallel collection defines:
def splitter: IterableSplitter[T]which returns an instance of
IterableSplitter[T], which is a subtype ofSplitter[T]. Splitters have a methodremainingto check the remaining number of elements, and methodsplitwhich is defined by splitters. Methodsplitdivides the splitters iterate over into disjunct subsets:which splits the splitter into a sequence of disjunct subsplitters. This is typically a very fast operation which simply creates wrappers around the receiver collection. This can be repeated recursively.
Tasks are scheduled for execution through a scala.collection.parallel.TaskSupport object, which can be changed through the
tasksupportsetter of the collection.Method
newCombinerproduces a new combiner. Combiners are an extension of builders. They provide a methodcombinewhich combines two combiners and returns a combiner containing elements of both combiners. This method can be implemented by aggressively copying all the elements into the new combiner or by lazily binding their results. It is recommended to avoid copying all of the elements for performance reasons, although that cost might be negligible depending on the use case. Standard parallel collection combiners avoid copying when merging results, relying either on a two-step lazy construction or specific data-structure properties.Methods:
produce the sequential or parallel implementation of the collection, respectively. Method
parjust returns a reference to this parallel collection. Methodseqis efficient - it will not copy the elements. Instead, it will create a sequential version of the collection using the same underlying data structure. Note that this is not the case for sequential collections in general - they may copy the elements and produce a different underlying data structure.The combination of methods
toMap,toSeqortoSetalong withparandseqis a flexible way to change between different collection types.Since this trait extends the
GenIterabletrait, methods likesizemust also be implemented in concrete collections, whileiteratorforwards tosplitterby default.Each parallel collection is bound to a specific fork/join pool, on which dormant worker threads are kept. The fork/join pool contains other information such as the parallelism level, that is, the number of processors used. When a collection is created, it is assigned the default fork/join pool found in the
scala.parallelpackage object.Parallel collections are not necessarily ordered in terms of the
foreachoperation (seeTraversable). Parallel sequences have a well defined order for iterators - creating an iterator and traversing the elements linearly will always yield the same order. However, bulk operations such asforeach,maporfilteralways occur in undefined orders for all parallel collections.Existing parallel collection implementations provide strict parallel iterators. Strict parallel iterators are aware of the number of elements they have yet to traverse. It's also possible to provide non-strict parallel iterators, which do not know the number of elements remaining. To do this, the new collection implementation must override
isStrictSplitterCollectiontofalse. This will make some operations unavailable.To create a new parallel collection, extend the
ParIterabletrait, and implementsize,splitter,newCombinerandseq. Having an implicit combiner factory requires extending this trait in addition, as well as providing a companion object, as with regular collections.Method
sizeis implemented as a constant time operation for parallel collections, and parallel collection operations rely on this assumption.The higher-order functions passed to certain operations may contain side-effects. Since implementations of bulk operations may not be sequential, this means that side-effects may not be predictable and may produce data-races, deadlocks or invalidation of state if care is not taken. It is up to the programmer to either avoid using side-effects or to use some form of synchronization when accessing mutable data.
the element type of the collection
2.9