A template trait for parallel collections of type ParIterable[T].
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 ParIterable if 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 parallelIterator: ParIterableIterator[T]
which returns an instance of ParIterableIterator[T], which is a subtype of Splitter[T].
Parallel iterators have a method remaining to check the remaining number of elements,
and method split which is defined by splitters. Method split divides the splitters
iterate over into disjunct subsets:
def split: Seq[Splitter]
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.
Method newCombiner produces a new combiner. Combiners are an extension of builders.
They provide a method combine which 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:
def seq: Sequential
def par: Repr
produce the sequential or parallel implementation of the collection, respectively.
Method par just returns a reference to this parallel collection.
Method seq is 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, toSeq or toSet along with par and seq is a flexible
way to change between different collection types.
The method:
def threshold(sz: Int, p: Int): Int
provides an estimate on the minimum number of elements the collection has before the splitting stops and depends on the number of elements in the collection. A rule of the thumb is the number of elements divided by 8 times the parallelism level. This method may be overridden in concrete implementations if necessary.
Since this trait extends the Iterable trait, methods like size must also
be implemented in concrete collections, while iterator forwards to parallelIterator by
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.parallel package object.
Parallel collections are not necessarily ordered in terms of the foreach
operation (see Traversable). 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 as foreach, map or filter always 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
isStrictSplitterCollection to false. This will make some operations unavailable.
To create a new parallel collection, extend the ParIterable trait, and implement size, parallelIterator,
newCombiner and seq. Having an implicit combiner factory requires extending this trait in addition, as
well as providing a companion object, as with regular collections.
Method size is implemented as a constant time operation for parallel collections, and parallel collection
operations rely on this assumption.
the element type of the collection
the type of the actual collection containing the elements
2.9
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.
Standard accessor task that iterates over the elements of the collection.
Performs two tasks in parallel, and waits for both to finish.
Parallel iterators are split iterators that have additional accessor and
transformer methods defined in terms of methods next and hasNext.
The type implementing this traversable
Sequentially performs one task after another.
A stackable modification that ensures signal contexts get passed along the iterators.
A class supporting filtered operations.
o != arg0 is the same as !(o == (arg0)).
o != arg0 is the same as !(o == (arg0)).
the object to compare against this object for dis-equality.
false if the receiver object is equivalent to the argument; true otherwise.
[use case] Concatenates this iterable collection with the elements of a traversable collection.
Concatenates this iterable collection with the elements of a traversable collection.
the element type of the returned collection.
the traversable to append.
a new iterable collection which contains all elements of this iterable collection
followed by all elements of that.
Concatenates this iterable collection with the elements of a traversable collection.
Concatenates this iterable collection with the elements of a traversable collection.
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.
the traversable to append.
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.
a new collection of type That which contains all elements
of this iterable collection followed by all elements of that.
This overload exists because: for the implementation of ++: we should reuse that of ++ because many collections override it with more efficient versions.
This overload exists because: for the implementation of ++: we should reuse that of ++ because many collections override it with more efficient versions. Since TraversableOnce has no '++' method, we have to implement that directly, but Traversable and down can use the overload.
[use case] Concatenates this iterable collection with the elements of a traversable collection.
Concatenates this iterable collection with the elements of a traversable collection. It differs from ++ in that the right operand determines the type of the resulting collection rather than the left one.
the element type of the returned collection.
the traversable to append.
a new iterable collection which contains all elements of this iterable collection
followed by all elements of that.
Concatenates this iterable collection with the elements of a traversable collection.
Concatenates this iterable collection with the elements of a traversable collection. It differs from ++ in that the right operand determines the type of the resulting collection rather than the left one.
the element type of the returned collection.
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.
the traversable to append.
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.
a new collection of type That which contains all elements
of this iterable collection followed by all elements of that.
Applies a binary operator to a start value and all elements of this iterable collection, going left to right.
Applies a binary operator to a start value and all elements of this iterable collection, going left to right.
Note: /: is alternate syntax for foldLeft; z /: xs is the same as
xs foldLeft 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.
the result type of the binary operator.
the start value.
the binary operator.
the result of inserting op between consecutive elements of this iterable collection,
going left to right with the start value z on the left:
op(...op(op(z, x,,1,,), x,,2,,), ..., x,,n,,)
where x,,1,,, ..., x,,n,, are the elements of this iterable collection.
Applies a binary operator to all elements of this iterable collection and a start value, going right to left.
Applies a binary operator to all elements of this iterable collection 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.
the result type of the binary operator.
the start value
the binary operator
the result of inserting op between consecutive elements of this iterable collection,
going right to left with the start value z on the right:
op(x,,1,,, op(x,,2,,, ... op(x,,n,,, z)...))
where x,,1,,, ..., x,,n,, are the elements of this iterable collection.
o == arg0 is the same as if (o eq null) arg0 eq null else o.equals(arg0).
o == arg0 is the same as if (o eq null) arg0 eq null else o.equals(arg0).
the object to compare against this object for equality.
true if the receiver object is equivalent to the argument; false otherwise.
o == arg0 is the same as o.equals(arg0).
o == arg0 is the same as o.equals(arg0).
the object to compare against this object for equality.
true if the receiver object is equivalent to the argument; false otherwise.
Appends all elements of this iterable collection to a string builder.
Appends all elements of this iterable collection to a string builder.
The written text consists of the string representations (w.r.t. the method
toString) of all elements of this iterable collection without any separator string.
the string builder to which elements are appended.
the string builder b to which elements were appended.
Appends all elements of this iterable collection to a string builder using a separator string.
Appends all elements of this iterable collection to a string builder using a separator
string. The written text consists of the string representations (w.r.t.
the method toString) of all elements of this iterable collection, separated by the
string sep.
the string builder to which elements are appended.
the separator string.
the string builder b to which elements were appended.
Appends all elements of this iterable collection to a string builder using start, end, and separator strings.
Appends all elements of this iterable collection to a string builder using start, end,
and separator strings.
The written text begins with the string start and ends with the string
end. Inside, the string representations (w.r.t. the method toString)
of all elements of this iterable collection are separated by the string sep.
the string builder to which elements are appended.
the starting string.
the separator string.
the ending string.
the string builder b to which elements were appended.
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 list, while combop
would concatenate two lists 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)
an operator used to accumulate results within a partition
an associative operator used to combine results from different partitions
This method is used to cast the receiver object to be of type T0.
This method is used to 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 typed.
the receiver object.
Method called from equality methods, so that user-defined subclasses can refuse to be equal to other collections of the same kind.
Method called from equality methods, so that user-defined subclasses can refuse to be equal to other collections of the same kind.
The object with which this iterable collection should be compared
true, if this iterable collection can possibly equal that, false otherwise. The test
takes into consideration only the run-time types of objects but ignores their elements.
This method creates and returns a copy of the receiver object.
[use case] Builds a new collection by applying a partial function to all elements of this iterable collection on which the function is defined.
Builds a new collection by applying a partial function to all elements of this iterable collection on which the function is defined.
the element type of the returned collection.
the partial function which filters and maps the iterable collection.
a new iterable 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.
Builds a new collection by applying a partial function to all elements of this iterable collection on which the function is defined.
Builds a new collection by applying a partial function to all elements of this iterable collection on which the function is defined.
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.
the partial function which filters and maps the iterable collection.
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.
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.
Finds the first element of the iterable collection for which the given partial function is defined, and applies the partial function to it.
Finds the first element of the iterable collection for which the given partial function is defined, and applies the partial function to it.
Note: may not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the underlying collection type is ordered.
the partial function
an option value containing pf applied to the first
value for which it is defined, or None if none exists.
Seq("a", 1, 5L).collectFirst({ case x: Int => x*10 }) = Some(10)
[use case] Copies elements of this iterable collection to an array.
Copies elements of this iterable collection to an array.
Fills the given array xs with at most len elements of
this iterable collection, starting at position start.
Copying will stop once either the end of the current iterable collection is reached,
or the end of the array is reached, or len elements have been copied.
the array to fill.
the starting index.
the maximal number of elements to copy.
Copies elements of this iterable collection to an array.
Copies elements of this iterable collection to an array.
Fills the given array xs with at most len elements of
this iterable collection, starting at position start.
Copying will stop once either the end of the current iterable collection is reached,
or the end of the array is reached, or len elements have been copied.
Note: will not terminate for infinite-sized collections.
the array to fill.
the starting index.
the maximal number of elements to copy.
[use case] Copies values of this iterable collection to an array.
Copies values of this iterable collection to an array.
Fills the given array xs with values of this iterable collection.
Copying will stop once either the end of the current iterable collection is reached,
or the end of the array is reached.
the array to fill.
Copies values of this iterable collection to an array.
Copies values of this iterable collection to an array.
Fills the given array xs with values of this iterable collection.
Copying will stop once either the end of the current iterable collection is reached,
or the end of the array is reached.
Note: will not terminate for infinite-sized collections.
the type of the elements of the array.
the array to fill.
[use case] Copies values of this iterable collection to an array.
Copies values of this iterable collection to an array.
Fills the given array xs with values of this iterable collection, after skipping start values.
Copying will stop once either the end of the current iterable collection is reached,
or the end of the array is reached.
the array to fill.
the starting index.
Copies values of this iterable collection to an array.
Copies values of this iterable collection to an array.
Fills the given array xs with values of this iterable collection, after skipping start values.
Copying will stop once either the end of the current iterable collection is reached,
or the end of the array is reached.
Note: will not terminate for infinite-sized collections.
the type of the elements of the array.
the array to fill.
the starting index.
Copies all elements of this iterable collection to a buffer.
Copies all elements of this iterable collection to a buffer.
Note: will not terminate for infinite-sized collections.
The buffer to which elements are copied.
Counts the number of elements in the iterable collection which satisfy a predicate.
Counts the number of elements in the iterable collection 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 iterable collection.
a iterable collection consisting of all elements of this iterable collection except the first n ones, or else the
empty iterable collection, if this iterable collection has less than n elements.
Selects all elements except last n ones.
Selects all elements except last n ones.
Note: might return different results for different runs, unless the underlying collection type is ordered.
The number of elements to take
a iterable collection consisting of all elements of this iterable collection except the last n ones, or else the
empty iterable collection, if this iterable collection has less than n elements.
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 iterable collection that satisfy the predicate pred
use iterator' instead
This method is used to test whether the argument (arg0) is a reference to the
receiver object (this).
This method is used to test whether the argument (arg0) is a reference to the
receiver object (this).
The eq method implements an [http://en.wikipedia.org/wiki/Equivalence_relation equivalence relation] on
non-null instances of AnyRef:
* It is reflexive: for any non-null instance x of type AnyRef, x.eq(x) returns true.
* It is symmetric: for any non-null instances x and y of type AnyRef, x.eq(y) returns true if and
only if y.eq(x) returns true.
* It is transitive: for any non-null instances x, y, and z of type AnyRef if x.eq(y) returns true
and y.eq(z) returns true, then x.eq(z) returns true.
Additionally, the eq method has three other properties.
* It is consistent: for any non-null instances x and y of type AnyRef, multiple invocations of
x.eq(y) consistently returns true or consistently returns false.
* For any non-null instance 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).
the object to compare against this object for reference equality.
true if the argument is a reference to the receiver object; false otherwise.
This method is used to compare the receiver object (this) with the argument object (arg0) for equivalence.
This method is used to compare the receiver object (this) with the argument object (arg0) for equivalence.
The default implementations of this method is an [http://en.wikipedia.org/wiki/Equivalence_relation equivalence
relation]:
* It is reflexive: for any instance x of type Any, x.equals(x) should return true.
* It is symmetric: for any instances x and y of type Any, x.equals(y) should return true if and
only if y.equals(x) returns true.
* It is transitive: for any instances x, y, and z of type AnyRef if x.equals(y) returns true and
y.equals(z) returns true, then x.equals(z) should return true.
If you override this method, you should verify that your implementation remains an equivalence relation.
Additionally, when overriding this method it is often necessary to override hashCode to ensure that objects
that are "equal" (o1.equals(o2) returns true) hash to the same Int
(o1.hashCode.equals(o2.hashCode)).
the object to compare against this object for equality.
true if the receiver object is equivalent to the argument; false otherwise.
Tests whether a predicate holds for some element of this iterable collection.
Tests whether a predicate holds for some element of this iterable collection.
This method will use abort signalling capabilities. This means
that splitters may send and read abort signals.
true if p holds for some element, false otherwise
Selects all elements of this iterable collection which satisfy a predicate.
Selects all elements of this iterable collection which satisfy a predicate.
a new iterable collection consisting of all elements of this iterable collection that satisfy the given
predicate p. The order of the elements is preserved.
Selects all elements of this iterable collection which do not satisfy a predicate.
Selects all elements of this iterable collection which do not satisfy a predicate.
a new iterable collection consisting of all elements of this iterable collection that do not satisfy the given
predicate p. The order of the elements is preserved.
This method is called by the garbage collector on the receiver object when garbage collection determines that there are no more references to the object.
This method is called by the garbage collector on the receiver object when garbage collection determines that there are no more references to the object.
The details of when and if the finalize method are 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.
an option value with the element if such an element exists, or None otherwise
use head' instead
None if iterable is empty.
None if iterable is empty.
use headOption' instead
[use case] Builds a new collection by applying a function to all elements of this iterable collection and concatenating the results.
Builds a new collection by applying a function to all elements of this iterable collection and concatenating the results.
the element type of the returned collection.
the function to apply to each element.
a new iterable collection resulting from applying the given collection-valued function
f to each element of this iterable collection and concatenating the results.
Builds a new collection by applying a function to all elements of this iterable collection and concatenating the results.
Builds a new collection by applying a function to all elements of this iterable collection and concatenating the results.
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.
the function to apply to each 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.
a new collection of type That resulting from applying the given collection-valued function
f to each element of this iterable collection and concatenating the results.
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 iterable collection, going left to right.
Applies a binary operator to a start value and all elements of this iterable collection, 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 iterable collection,
going left to right with the start value z on the left:
op(...op(z, x,,1,,), x,,2,,, ..., x,,n,,)
where x,,1,,, ..., x,,n,, are the elements of this iterable collection.
Applies a binary operator to all elements of this iterable collection and a start value, going right to left.
Applies a binary operator to all elements of this iterable collection and a start value, going right to left.
Note: will not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the underlying collection type is ordered. or the operator is associative and commutative.
the start value.
the binary operator.
the result of inserting op between consecutive elements of this iterable collection,
going right to left with the start value z on the right:
op(x,,1,,, op(x,,2,,, ... op(x,,n,,, z)...))
where x,,1,,, ..., x,,n,, are the elements of this iterable collection.
Tests whether a predicate holds for all elements of this iterable collection.
Tests whether a predicate holds for all elements of this iterable collection.
This method will use abort signalling capabilities. This means
that splitters may send and read abort signals.
true if p holds for all elements, false otherwise
Applies a function f to all the elements of iterable collection in a sequential order.
Applies a function f to all the elements of iterable collection in a sequential order.
the result type of the function applied to each element, which is always discarded
function applied to each element
Returns a representation that corresponds to the dynamic class of the receiver object.
Returns 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.
Partitions this iterable collection into a map of iterable collections according to some discriminator function.
Partitions this iterable collection into a map of iterable 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 iterable collection.
the type of keys returned by the discriminator function.
the discriminator function.
A map from keys to iterable collections such that the following invariant holds:
(xs partition f)(k) = xs filter (x => f(x) == k)
That is, every key k is bound to a iterable collection of those elements x
for which f(x) equals k.
Partitions elements in fixed size iterable collections.
Partitions elements in fixed size iterable collections.
the number of elements per group
An iterator producing iterable collections of size size, except the
last will be truncated if the elements don't divide evenly.
Iterator#grouped
Tests whether this iterable collection is known to have a finite size.
Tests whether this iterable collection is known to have a finite size.
All strict collections are known to have finite size. For a non-strict collection
such as Stream, the predicate returns true if all elements have been computed.
It returns false if the stream is not yet evaluated to the end.
Note: many collection methods will not work on collections of infinite sizes.
true if this collection is known to have finite size, false otherwise.
Returns a hash code value for the object.
Returns a hash code value for the object.
The default hashing algorithm is platform dependent.
Note that it is allowed for two objects to have identical hash codes (o1.hashCode.equals(o2.hashCode)) yet
not be equal (o1.equals(o2) returns false). A degenerate implementation could always return 0.
However, it is required that if two objects are equal (o1.equals(o2) returns true) that they have
identical hash codes (o1.hashCode.equals(o2.hashCode)). Therefore, when overriding this method, be sure
to verify that the behavior is consistent with the equals method.
the hash code value for the object.
Selects the first element of this iterable collection.
Selects the first element of this iterable collection.
Note: might return different results for different runs, unless the underlying collection type is ordered.
the first element of this iterable collection.
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 iterable collection 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 iterable collection consisting of all elements of this iterable collection except the last one.
Iterates over the inits of this iterable collection.
Iterates over the inits of this iterable collection. The first value will be this
iterable collection and the final one will be an empty iterable collection, with the intervening
values the results of successive applications of init.
an iterator over all the inits of this iterable collection
List(1,2,3).inits = Iterator(List(1,2,3), List(1,2), List(1), Nil)
Tests whether this iterable collection is empty.
Tests whether this iterable collection is empty.
true if the iterable collection contain no elements, false otherwise.
This method is used to test whether the dynamic type of the receiver object is T0.
This method is used to test whether the dynamic type of the receiver object is T0.
Note that the test 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 requested typed.
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 iterable collection can be repeatedly traversed.
Tests whether this iterable collection 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 parallelIterator 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 iterable collection.
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 iterable collection$ if it is nonempty, None if it is empty.
[use case] Builds a new collection by applying a function to all elements of this iterable collection.
Builds a new collection by applying a function to all elements of this iterable collection.
the element type of the returned collection.
the function to apply to each element.
a new iterable collection resulting from applying the given function
f to each element of this iterable collection and collecting the results.
Builds a new collection by applying a function to all elements of this iterable collection.
Builds a new collection by applying a function to all elements of this iterable collection.
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.
the function to apply to each 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.
a new collection of type That resulting from applying the given function
f to each element of this iterable collection and collecting the results.
[use case] Finds the largest element.
Finds the largest element.
the largest element of this iterable collection.
Finds the largest element.
Finds the largest element.
the largest element of this iterable collection with respect to the ordering cmp.
[use case] Finds the smallest element.
Finds the smallest element.
the smallest element of this iterable collection
Finds the smallest element.
Finds the smallest element.
the smallest element of this iterable collection with respect to the ordering cmp.
Displays all elements of this iterable collection in a string.
Displays all elements of this iterable collection in a string.
a string representation of this iterable collection. In the resulting string
the string representations (w.r.t. the method toString)
of all elements of this iterable collection follow each other without any
separator string.
Displays all elements of this iterable collection in a string using a separator string.
Displays all elements of this iterable collection in a string using a separator string.
the separator string.
a string representation of this iterable collection. In the resulting string
the string representations (w.r.t. the method toString)
of all elements of this iterable collection are separated by the string sep.
List(1, 2, 3).mkString("|") = "1|2|3"
Displays all elements of this iterable collection in a string using start, end, and separator strings.
Displays all elements of this iterable collection in a string using start, end, and separator strings.
the starting string.
the separator string.
the ending string.
a string representation of this iterable collection. 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 iterable collection are separated by
the string sep.
List(1, 2, 3).mkString("(", "; ", ")") = "(1; 2; 3)"
o.ne(arg0) is the same as !(o.eq(arg0)).
o.ne(arg0) is the same as !(o.eq(arg0)).
the object to compare against this object for reference dis-equality.
false if the argument is not a reference to the receiver object; true otherwise.
The newBuilder operation returns a parallel builder assigned to this collection's fork/join pool.
The newBuilder operation returns a parallel builder assigned to this collection's fork/join pool.
This method forwards the call to newCombiner.
Tests whether the iterable collection is not empty.
Tests whether the iterable collection is not empty.
true if the iterable collection 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.
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.
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
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
Partitions this iterable collection in two iterable collections according to a predicate.
Partitions this iterable collection in two iterable collections according to a predicate.
a pair of iterable collections: the first iterable collection consists of all elements that
satisfy the predicate p and the second iterable collection consists of all elements
that don't. The relative order of the elements in the resulting iterable collections
is the same as in the original iterable collection.
[use case] Multiplies up the elements of this collection.
Multiplies up the elements of this collection.
the product of all elements in this iterable collection 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 iterable collection and as result type of product.
Examples of such types are: Long, Float, Double, BigInt.
Multiplies up the elements of this collection.
Multiplies up the elements of this collection.
an implicit parameter defining a set of numeric operations
which includes the * operator to be used in forming the product.
the product of all elements of this iterable collection with respect to the * operator in num.
returns a projection that can be used to call non-strict filter,
map, and flatMap methods that build projections
of the collection.
returns a projection that can be used to call non-strict filter,
map, and flatMap methods that build projections
of the collection.
use view' instead
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 the operations on elements are performed 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.
Applies a binary operator to all elements of this iterable collection, going left to right.
Applies a binary operator to all elements of this iterable collection, 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.
the result of inserting op between consecutive elements of this iterable collection,
going left to right:
op(...(op(x,,1,,, x,,2,,), ... ) , x,,n,,)
where x,,1,,, ..., x,,n,, are the elements of this iterable collection.
Optionally applies a binary operator to all elements of this iterable collection, going left to right.
Optionally applies a binary operator to all elements of this iterable collection, 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 result type of the binary operator.
the binary operator.
an option value containing the result of reduceLeft(op) is this iterable collection 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 the operations on elements are performed 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 iterable collection, going right to left.
Applies a binary operator to all elements of this iterable collection, going right to left.
Note: will not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the underlying collection type is ordered. or the operator is associative and commutative.
the binary operator.
the result of inserting op between consecutive elements of this iterable collection,
going right to left:
op(x,,1,,, op(x,,2,,, ..., op(x,,n-1,,, x,,n,,)...))
where x,,1,,, ..., x,,n,, are the elements of this iterable collection.
Optionally applies a binary operator to all elements of this iterable collection, going right to left.
Optionally applies a binary operator to all elements of this iterable collection, going right to left.
Note: will not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the underlying collection type is ordered. or the operator is associative and commutative.
the result type of the binary operator.
the binary operator.
an option value containing the result of reduceRight(op) is this iterable collection is nonempty,
None otherwise.
The collection of type iterable collection underlying this TraversableLike object.
The collection of type iterable collection underlying this TraversableLike object.
By default this is implemented as the TraversableLike object itself,
but this can be overridden.
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 iterable collection.
Checks if the other iterable collection contains the same elements in the same order as this iterable collection.
the collection to compare with.
true, if both collections contain the same elements in the same order, false otherwise.
Checks if the other iterable collection contains the same elements in the same order as this iterable collection.
Checks if the other iterable collection contains the same elements in the same order as this iterable collection.
Note: might return different results for different runs, unless the underlying collection type is ordered.
Note: will not terminate for infinite-sized collections.
the type of the elements of collection that.
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.
neutral element for the operator op
the associative operator for the scan
a new iterable collection containing the prefix scan of the elements in this iterable collection
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.
element type of the resulting collection
type of the resulting collection
neutral element for the operator op
the associative operator for the scan
combiner factory which provides a combiner
a collection containing the prefix scan of the elements in the original collection
Produces a collection containing cummulative results of applying the operator going left to right.
Produces a collection containing cummulative 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 type of the elements in the resulting collection
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 cummulative results of applying the operator going right to left.
Produces a collection containing cummulative results of applying the operator going right to left. The head of the collection is the last cummulative 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 type of the elements in the resulting collection
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
A version of this collection with all of the operations implemented sequentially (i.
A version of this collection with all of the operations implemented sequentially (i.e. in a single-threaded manner).
This method returns a reference to this collection. In parallel collections, it is redefined to return a sequential implementation of this collection. In both cases, it has O(1) complexity.
a sequential view of the collection.
The size of this iterable collection.
The size of this iterable collection.
Note: will not terminate for infinite-sized collections.
the number of elements in this iterable collection.
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.
a iterable collection containing the elements greater than or equal to
index from extending up to (but not including) index until
of this iterable collection.
Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.
Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.)
the number of elements per group
An iterator producing iterable collections of size size, except the
last and the only element will be truncated if there are
fewer elements than size.
Iterator#sliding
Splits this iterable collection into a prefix/suffix pair according to a predicate.
Splits this iterable collection 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 iterable collection into two at a given position.
Splits this iterable 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.
the position at which to split.
a pair of iterable collections consisting of the first n
elements of this iterable collection, 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 iterable collection. By default the string prefix is the
simple name of the collection class iterable collection.
[use case] Sums up the elements of this collection.
Sums up the elements of this collection.
the sum of all elements in this iterable collection 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 iterable collection and as result type of sum.
Examples of such types are: Long, Float, Double, BigInt.
Sums up the elements of this collection.
Sums up the elements of this collection.
an implicit parameter defining a set of numeric operations
which includes the + operator to be used in forming the sum.
the sum of all elements of this iterable collection with respect to the + operator in num.
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 iterable collection consisting of all elements of this iterable collection except the first one.
Iterates over the tails of this iterable collection.
Iterates over the tails of this iterable collection. The first value will be this
iterable collection and the final one will be an empty iterable collection, with the intervening
values the results of successive applications of tail.
an iterator over all the tails of this iterable collection
List(1,2,3).tails = Iterator(List(1,2,3), List(2,3), List(3), Nil)
Selects first n elements.
Selects first n elements.
Note: might return different results for different runs, unless the underlying collection type is ordered.
Tt number of elements to take from this iterable collection.
a iterable collection consisting only of the first n elements of this iterable collection,
or else the whole iterable collection, if it has less than n elements.
Selects last n elements.
Selects last n elements.
Note: might return different results for different runs, unless the underlying collection type is ordered.
the number of elements to take
a iterable collection consisting only of the last n elements of this iterable collection, or else the
whole iterable collection, if it has less than n elements.
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 iterable collection of elements that satisy the predicate pred
The underlying collection seen as an instance of Iterable.
The underlying collection seen as an instance of Iterable.
By default this is implemented as the current collection object itself,
but this can be overridden.
Some minimal number of elements after which this collection should be handled sequentially by different processors.
Some minimal number of elements after which this collection should be handled sequentially by different processors.
This method depends on the size of the collection and the parallelism level, which are both specified as arguments.
the size based on which to compute the threshold
the parallelism level based on which to compute the threshold
the maximum number of elements for performing operations sequentially
[use case] Converts this iterable collection to an array.
Converts this iterable collection to an array.
Note: will not terminate for infinite-sized collections.
an array containing all elements of this iterable collection.
A ClassManifest must be available for the element type of this iterable collection.
Converts this iterable collection to an array.
Converts this iterable collection to an array.
Note: will not terminate for infinite-sized collections.
an array containing all elements of this iterable collection.
Converts this iterable collection to a mutable buffer.
Converts this iterable collection to a mutable buffer.
Note: will not terminate for infinite-sized collections.
a buffer containing all elements of this iterable collection.
A conversion from collections of type Repr to Iterable objects.
A conversion from collections of type Repr to Iterable objects.
By default this is implemented as just a cast, but this can be overridden.
Converts this iterable collection to an indexed sequence.
Converts this iterable collection to an indexed sequence.
Note: will not terminate for infinite-sized collections.
an indexed sequence containing all elements of this iterable collection.
Converts this iterable collection to an iterable collection.
Converts this iterable collection 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 iterable collection.
Returns an Iterator over the elements in this iterable collection.
Returns an Iterator over the elements in this iterable collection. 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 iterable collection.
Converts this iterable collection to a list.
Converts this iterable collection to a list.
Note: will not terminate for infinite-sized collections.
a list containing all elements of this iterable collection.
[use case] Converts this iterable collection to a map.
Converts this iterable 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.
a map of type immutable.Map[T, U]
containing all key/value pairs of type (T, U) of this iterable collection.
Converts this iterable collection to a map.
Converts this iterable 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.
a map containing all elements of this iterable collection.
Converts this iterable collection to a sequence.
Converts this iterable collection 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 iterable collection.
Converts this iterable collection to a set.
Converts this iterable collection to a set.
Note: will not terminate for infinite-sized collections.
a set containing all elements of this iterable collection.
Converts this iterable collection to a stream.
Converts this iterable collection to a stream.
Note: will not terminate for infinite-sized collections.
a stream containing all elements of this iterable collection.
Converts this iterable collection to a string.
Converts this iterable collection to a string.
a string representation of this collection. By default this
string consists of the stringPrefix of this iterable collection,
followed by all elements separated by commas and enclosed in parentheses.
Converts this iterable collection to an unspecified Traversable.
Converts this iterable collection 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 iterable collection.
Creates a non-strict view of this iterable collection.
Creates a non-strict view of this iterable collection.
a non-strict view of this iterable collection.
Creates a non-strict view of a slice of this iterable collection.
Creates a non-strict view of a slice of this iterable collection.
Note: the difference between view and slice is that view produces
a view of the current iterable collection, whereas slice produces a new iterable collection.
Note: view(from, to) is equivalent to view.slice(from, to)
Note: might return different results for different runs, unless the underlying collection type is ordered.
the index of the first element of the view
the index of the element following the view
a non-strict view of a slice of this iterable collection, starting at index from
and extending up to (but not including) index until.
Creates a non-strict filter of this iterable collection.
Creates a non-strict filter of this iterable collection.
Note: the difference between c filter p and c withFilter p is that
the former creates a new collection, whereas the latter only
restricts the domain of subsequent map, flatMap, foreach,
and withFilter operations.
Note: might return different results for different runs, unless the underlying collection type is ordered.
the predicate used to test elements.
an object of class WithFilter, which supports
map, flatMap, foreach, and withFilter operations.
All these operations apply to those elements of this iterable collection which
satisfy the predicate p.
[use case] Returns a iterable collection formed from this iterable collection and another iterable collection by combining corresponding elements in pairs.
Returns a iterable collection formed from this iterable collection 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.
the type of the second half of the returned pairs
The iterable providing the second half of each result pair
a new iterable collection containing pairs consisting of
corresponding elements of this iterable collection and that. The length
of the returned collection is the minimum of the lengths of this iterable collection and that.
Returns a iterable collection formed from this iterable collection and another iterable collection by combining corresponding elements in pairs.
Returns a iterable collection formed from this iterable collection 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 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 (A1, B) being admissible for that class,
which means that an implicit instance of type CanBuildFrom[Repr, (A1, B), That].
is found.
The iterable providing the second half of each result pair
an implicit value of class CanBuildFrom which determines the
result class That from the current representation type Repr
and the new element type (A1, B).
a new collection of type That containing pairs consisting of
corresponding elements of this iterable collection and that. The length
of the returned collection is the minimum of the lengths of this iterable collection and that.
[use case] Returns a iterable collection formed from this iterable collection and another iterable collection by combining corresponding elements in pairs.
Returns a iterable collection formed from this iterable collection 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.
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 iterable collection is shorter than that.
the element to be used to fill up the result if that is shorter than this iterable collection.
a new iterable collection containing pairs consisting of
corresponding elements of this iterable collection and that. The length
of the returned collection is the maximum of the lengths of this iterable collection and that.
If this iterable collection is shorter than that, thisElem values are used to pad the result.
If that is shorter than this iterable collection, thatElem values are used to pad the result.
Returns a iterable collection formed from this iterable collection and another iterable collection by combining corresponding elements in pairs.
Returns a iterable collection formed from this iterable collection 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 iterable providing the second half of each result pair
the element to be used to fill up the result if this iterable collection is shorter than that.
the element to be used to fill up the result if that is shorter than this iterable collection.
a new collection of type That containing pairs consisting of
corresponding elements of this iterable collection and that. The length
of the returned collection is the maximum of the lengths of this iterable collection and that.
If this iterable collection is shorter than that, thisElem values are used to pad the result.
If that is shorter than this iterable collection, thatElem values are used to pad the result.
[use case] Zips this iterable collection with its indices.
Zips this iterable collection with its indices.
A new iterable collection containing pairs consisting of all elements of this
iterable collection paired with their index. Indices start at 0.
@example
List("a", "b", "c").zipWithIndex = List(("a", 0), ("b", 1), ("c", 2))
Zips this iterable collection with its indices.
Zips this iterable collection with its indices.
Note: might return different results for different runs, unless the underlying collection type is ordered.
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 (A1, Int) being admissible for that class,
which means that an implicit instance of type CanBuildFrom[Repr, (A1, Int), That].
is found.
A new collection of type That containing pairs consisting of all elements of this
iterable collection paired with their index. Indices start at 0.
A template trait for parallel collections of type
ParIterable[T].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 parallelIterator: ParIterableIterator[T]which returns an instance of
ParIterableIterator[T], which is a subtype ofSplitter[T]. Parallel iterators have a methodremainingto check the remaining number of elements, and methodsplitwhich is defined by splitters. Methodsplitdivides the splitters iterate over into disjunct subsets:def split: Seq[Splitter]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.
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:
def seq: Sequential def par: Reprproduce 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.The method:
def threshold(sz: Int, p: Int): Intprovides an estimate on the minimum number of elements the collection has before the splitting stops and depends on the number of elements in the collection. A rule of the thumb is the number of elements divided by 8 times the parallelism level. This method may be overridden in concrete implementations if necessary.
Since this trait extends the
Iterabletrait, methods likesizemust also be implemented in concrete collections, whileiteratorforwards toparallelIteratorby 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,parallelIterator,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.