MoreCollectors (StreamEx 0.6.5 API)

Object
- MoreCollectors

```
public final class MoreCollectors
extends Object
```
Implementations of several collectors in addition to ones available in JDK.

Since:

0.3.2

Author:

Tagir Valeev

See Also:

Collectors, Joining

Method Summary

All Methods Static Methods Concrete Methods
Modifier and Type	Method and Description
`static <T> Collector<T,?,OptionalInt>`	`andingInt(ToIntFunction<T> mapper)` Returns a `Collector` which performs the bitwise-and operation of a integer-valued function applied to the input elements.
`static <T> Collector<T,?,OptionalLong>`	`andingLong(ToLongFunction<T> mapper)` Returns a `Collector` which performs the bitwise-and operation of a long-valued function applied to the input elements.
`static <T,A,R,RR> Collector<T,A,RR>`	`collectingAndThen(Collector<T,A,R> downstream, Function<R,RR> finisher)` Adapts a `Collector` to perform an additional finishing transformation.
`static Collector<CharSequence,?,String>`	`commonPrefix()` Returns a `Collector` which computes a common prefix of input `CharSequence` objects returning the result as `String`.
`static Collector<CharSequence,?,String>`	`commonSuffix()` Returns a `Collector` which computes a common suffix of input `CharSequence` objects returning the result as `String`.
`static <T> Collector<T,?,Integer>`	`countingInt()` Returns a `Collector` accepting elements of type `T` that counts the number of input elements and returns result as `Integer` .
`static <T> Collector<T,?,List<T>>`	`distinctBy(Function<? super T,?> mapper)` Returns a `Collector` which collects into the `List` the input elements for which given mapper function returns distinct results.
`static <T> Collector<T,?,Integer>`	`distinctCount(Function<? super T,?> mapper)` Returns a `Collector` which counts a number of distinct values the mapper function returns for the stream elements.
`static <T> Collector<T,?,List<T>>`	`dominators(BiPredicate<? super T,? super T> isDominator)` Returns a collector which collects input elements into `List` removing the elements following their dominator element.
`static <T> Collector<T,?,List<T>>`	`filtering(Predicate<? super T> predicate)` Returns a `Collector` which filters input elements by the supplied predicate, collecting them to the list.
`static <T,A,R> Collector<T,?,R>`	`filtering(Predicate<? super T> predicate, Collector<T,A,R> downstream)` Returns a `Collector` which passes only those elements to the specified downstream collector which match given predicate.
`static <T> Collector<T,?,Optional<T>>`	`first()` Returns a `Collector` which collects only the first stream element if any.
`static <T,U> Collector<T,?,List<U>>`	`flatMapping(Function<? super T,? extends Stream<? extends U>> mapper)` Returns a collector which launches a flat mapping function for each input element and collects the elements of the resulting streams to the flat `List`.
`static <T,U,A,R> Collector<T,?,R>`	`flatMapping(Function<? super T,? extends Stream<? extends U>> mapper, Collector<? super U,A,R> downstream)` Adapts a `Collector` accepting elements of type `U` to one accepting elements of type `T` by applying a flat mapping function to each input element before accumulation.
`static <T> Collector<T,?,List<T>>`	`greatest(Comparator<? super T> comparator, int n)` Returns a `Collector` which collects at most specified number of the greatest stream elements according to the specified `Comparator` into the `List`.
`static <T extends Comparable<? super T>> Collector<T,?,List<T>>`	`greatest(int n)` Returns a `Collector` which collects at most specified number of the greatest stream elements according to the natural order into the `List`.
`static <T,K,D,A> Collector<T,?,Map<K,D>>`	`groupingBy(Function<? super T,? extends K> classifier, Set<K> domain, Collector<? super T,A,D> downstream)` Returns a `Collector` implementing a cascaded "group by" operation on input elements of type `T`, grouping elements according to a classification function, and then performing a reduction operation on the values associated with a given key using the specified downstream `Collector`.
`static <T,K,D,A,M extends Map<K,D>> Collector<T,?,M>`	`groupingBy(Function<? super T,? extends K> classifier, Set<K> domain, Supplier<M> mapFactory, Collector<? super T,A,D> downstream)` Returns a `Collector` implementing a cascaded "group by" operation on input elements of type `T`, grouping elements according to a classification function, and then performing a reduction operation on the values associated with a given key using the specified downstream `Collector`.
`static <T,K extends Enum<K>,A,D> Collector<T,?,EnumMap<K,D>>`	`groupingByEnum(Class<K> enumClass, Function<? super T,K> classifier, Collector<? super T,A,D> downstream)` Returns a `Collector` implementing a cascaded "group by" operation on input elements of type `T`, for classification function which maps input elements to the enum values.
`static <T> Collector<T,?,List<T>>`	`head(int n)` Returns a `Collector` which collects at most specified number of the first stream elements into the `List`.
`static <T,A,R> Collector<T,?,Optional<R>>`	`ifAllMatch(Predicate<T> predicate, Collector<T,A,R> downstream)` Returns a `Collector` which performs downstream reduction if all elements satisfy the `Predicate`.
`static <T,S extends Collection<T>> Collector<S,?,Set<T>>`	`intersecting()` Returns a `Collector` which collects the intersection of the input collections into the newly-created `Set`.
`static <T> Collector<T,?,Optional<T>>`	`last()` Returns a `Collector` which collects only the last stream element if any.
`static <T> Collector<T,?,List<T>>`	`least(Comparator<? super T> comparator, int n)` Returns a `Collector` which collects at most specified number of the least stream elements according to the specified `Comparator` into the `List`.
`static <T extends Comparable<? super T>> Collector<T,?,List<T>>`	`least(int n)` Returns a `Collector` which collects at most specified number of the least stream elements according to the natural order into the `List`.
`static <T,U> Collector<T,?,List<U>>`	`mapping(Function<? super T,? extends U> mapper)` Returns a collector which collects input elements to the new `List` transforming them with the supplied function beforehand.
`static <T,U,A,R> Collector<T,?,R>`	`mapping(Function<? super T,? extends U> mapper, Collector<? super U,A,R> downstream)` Adapts a `Collector` accepting elements of type `U` to one accepting elements of type `T` by applying a mapping function to each input element before accumulation.
`static <T extends Comparable<? super T>> Collector<T,?,List<T>>`	`maxAll()` Returns a `Collector` which finds all the elements which are equal to each other and bigger than any other element according to the natural order.
`static <T extends Comparable<? super T>,A,D> Collector<T,?,D>`	`maxAll(Collector<T,A,D> downstream)` Returns a `Collector` which finds all the elements which are equal to each other and bigger than any other element according to the natural order.
`static <T> Collector<T,?,List<T>>`	`maxAll(Comparator<? super T> comparator)` Returns a `Collector` which finds all the elements which are equal to each other and bigger than any other element according to the specified `Comparator`.
`static <T,A,D> Collector<T,?,D>`	`maxAll(Comparator<? super T> comparator, Collector<? super T,A,D> downstream)` Returns a `Collector` which finds all the elements which are equal to each other and bigger than any other element according to the specified `Comparator`.
`static <T extends Comparable<? super T>> Collector<T,?,OptionalLong>`	`maxIndex()` Returns a `Collector` which finds the index of the maximal stream element according to the elements natural order.
`static <T> Collector<T,?,OptionalLong>`	`maxIndex(Comparator<? super T> comparator)` Returns a `Collector` which finds the index of the maximal stream element according to the specified `Comparator`.
`static <T extends Comparable<? super T>> Collector<T,?,List<T>>`	`minAll()` Returns a `Collector` which finds all the elements which are equal to each other and smaller than any other element according to the natural order.
`static <T extends Comparable<? super T>,A,D> Collector<T,?,D>`	`minAll(Collector<T,A,D> downstream)` Returns a `Collector` which finds all the elements which are equal to each other and smaller than any other element according to the natural order.
`static <T> Collector<T,?,List<T>>`	`minAll(Comparator<? super T> comparator)` Returns a `Collector` which finds all the elements which are equal to each other and smaller than any other element according to the specified `Comparator`.
`static <T,A,D> Collector<T,?,D>`	`minAll(Comparator<? super T> comparator, Collector<T,A,D> downstream)` Returns a `Collector` which finds all the elements which are equal to each other and smaller than any other element according to the specified `Comparator`.
`static <T extends Comparable<? super T>> Collector<T,?,OptionalLong>`	`minIndex()` Returns a `Collector` which finds the index of the minimal stream element according to the elements natural order.
`static <T> Collector<T,?,OptionalLong>`	`minIndex(Comparator<? super T> comparator)` Returns a `Collector` which finds the index of the minimal stream element according to the specified `Comparator`.
`static <T,R> Collector<T,?,Optional<R>>`	`minMax(Comparator<? super T> comparator, BiFunction<? super T,? super T,? extends R> finisher)` Returns a `Collector` which finds the minimal and maximal element according to the supplied comparator, then applies finisher function to them producing the final result.
`static <T> Collector<T,?,Optional<T>>`	`onlyOne()` Returns a `Collector` which collects the stream element if stream contains exactly one element.
`static <T,A1,A2,R1,R2,R> Collector<T,?,R>`	`pairing(Collector<? super T,A1,R1> c1, Collector<? super T,A2,R2> c2, BiFunction<? super R1,? super R2,? extends R> finisher)` Returns a `Collector` which aggregates the results of two supplied collectors using the supplied finisher function.
`static <T,D,A> Collector<T,?,Map<Boolean,D>>`	`partitioningBy(Predicate<? super T> predicate, Collector<? super T,A,D> downstream)` Returns a `Collector` which partitions the input elements according to a `Predicate`, reduces the values in each partition according to another `Collector`, and organizes them into a `Map<Boolean, D>` whose values are the result of the downstream reduction.
`static <T> Collector<T,?,List<T>>`	`tail(int n)` Returns a `Collector` which collects at most specified number of the last stream elements into the `List`.
`static <T> Collector<T,?,T[]>`	`toArray(IntFunction<T[]> generator)` Returns a `Collector` that accumulates the input elements into a new array.
`static <T> Collector<T,?,boolean[]>`	`toBooleanArray(Predicate<T> predicate)` Returns a `Collector` which produces a boolean array containing the results of applying the given predicate to the input elements, in encounter order.
`static <T extends Enum<T>> Collector<T,?,EnumSet<T>>`	`toEnumSet(Class<T> enumClass)` Returns a `Collector` that accumulates the input enum values into a new `EnumSet`.

Methods inherited from class Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Method Detail
  - toArray
```
public static <T> Collector<T,?,T[]> toArray(IntFunction<T[]> generator)
```
    Returns a Collector that accumulates the input elements into a new array. The operation performed by the returned collector is equivalent to stream.toArray(generator). This collector is mostly useful as a downstream collector.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Parameters:
    
    generator - a function which produces a new array of the desired type and the provided length
    
    Returns:
    
    a Collector which collects all the input elements into an array, in encounter order
  - toBooleanArray
```
public static <T> Collector<T,?,boolean[]> toBooleanArray(Predicate<T> predicate)
```
    Returns a Collector which produces a boolean array containing the results of applying the given predicate to the input elements, in encounter order.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Parameters:
    
    predicate - a non-interfering, stateless predicate to apply to each input element. The result values of this predicate are collected to the resulting boolean array.
    
    Returns:
    
    a Collector which collects the results of the predicate function to the boolean array, in encounter order.
    
    Since:
    
    0.3.8
  - toEnumSet
```
public static <T extends Enum<T>> Collector<T,?,EnumSet<T>> toEnumSet(Class<T> enumClass)
```
    Returns a Collector that accumulates the input enum values into a new EnumSet.
    This method returns a short-circuiting collector: it may not process all the elements if the resulting set contains all possible enum values.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Parameters:
    
    enumClass - the class of input enum values
    
    Returns:
    
    a Collector which collects all the input elements into a EnumSet
  - distinctCount
```
public static <T> Collector<T,?,Integer> distinctCount(Function<? super T,?> mapper)
```
    Returns a Collector which counts a number of distinct values the mapper function returns for the stream elements.
    The operation performed by the returned collector is equivalent to stream.map(mapper).distinct().count(). This collector is mostly useful as a downstream collector.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Parameters:
    
    mapper - a function which classifies input elements.
    
    Returns:
    
    a collector which counts a number of distinct classes the mapper function returns for the stream elements.
  - distinctBy
```
public static <T> Collector<T,?,List<T>> distinctBy(Function<? super T,?> mapper)
```
    Returns a Collector which collects into the List the input elements for which given mapper function returns distinct results.
    For ordered source the order of collected elements is preserved. If the same result is returned by mapper function for several elements, only the first element is included into the resulting list.
    There are no guarantees on the type, mutability, serializability, or thread-safety of the List returned.
    The operation performed by the returned collector is equivalent to stream.distinct(mapper).toList(), but may work faster.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Parameters:
    
    mapper - a function which classifies input elements.
    
    Returns:
    
    a collector which collects distinct elements to the List.
    
    Since:
    
    0.3.8
  - countingInt
```
public static <T> Collector<T,?,Integer> countingInt()
```
    Returns a Collector accepting elements of type T that counts the number of input elements and returns result as Integer . If no elements are present, the result is 0.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Returns:
    
    a Collector that counts the input elements
    
    Since:
    
    0.3.3
    
    See Also:
    
    Collectors.counting()
  - pairing
```
public static <T,A1,A2,R1,R2,R> Collector<T,?,R> pairing(Collector<? super T,A1,R1> c1,
                                                         Collector<? super T,A2,R2> c2,
                                                         BiFunction<? super R1,? super R2,? extends R> finisher)
```
    Returns a Collector which aggregates the results of two supplied collectors using the supplied finisher function.
    This method returns a short-circuiting collector if both downstream collectors are short-circuiting. The collection might stop when both downstream collectors report that the collection is complete.
    
    Type Parameters:
    
    T - the type of the input elements
    
    A1 - the intermediate accumulation type of the first collector
    
    A2 - the intermediate accumulation type of the second collector
    
    R1 - the result type of the first collector
    
    R2 - the result type of the second collector
    
    R - the final result type
    
    Parameters:
    
    c1 - the first collector
    
    c2 - the second collector
    
    finisher - the function which merges two results into the single one.
    
    Returns:
    
    a Collector which aggregates the results of two supplied collectors.
  - minMax
```
public static <T,R> Collector<T,?,Optional<R>> minMax(Comparator<? super T> comparator,
                                                      BiFunction<? super T,? super T,? extends R> finisher)
```
    Returns a Collector which finds the minimal and maximal element according to the supplied comparator, then applies finisher function to them producing the final result.
    This collector produces stable result for ordered stream: if several minimal or maximal elements appear, the collector always selects the first encountered.
    If there are no input elements, the finisher method is not called and empty Optional is returned. Otherwise the finisher result is wrapped into Optional.
    
    Type Parameters:
    
    T - the type of the input elements
    
    R - the type of the result wrapped into Optional
    
    Parameters:
    
    comparator - comparator which is used to find minimal and maximal element
    
    finisher - a BiFunction which takes minimal and maximal element and produces the final result.
    
    Returns:
    
    a Collector which finds minimal and maximal elements.
  - maxAll
```
public static <T,A,D> Collector<T,?,D> maxAll(Comparator<? super T> comparator,
                                              Collector<? super T,A,D> downstream)
```
    Returns a Collector which finds all the elements which are equal to each other and bigger than any other element according to the specified Comparator. The found elements are reduced using the specified downstream Collector.
    
    Type Parameters:
    
    T - the type of the input elements
    
    A - the intermediate accumulation type of the downstream collector
    
    D - the result type of the downstream reduction
    
    Parameters:
    
    comparator - a Comparator to compare the elements
    
    downstream - a Collector implementing the downstream reduction
    
    Returns:
    
    a Collector which finds all the maximal elements.
    
    See Also:
    
    maxAll(Comparator), maxAll(Collector), maxAll()
  - maxAll
```
public static <T> Collector<T,?,List<T>> maxAll(Comparator<? super T> comparator)
```
    Returns a Collector which finds all the elements which are equal to each other and bigger than any other element according to the specified Comparator. The found elements are collected to List.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Parameters:
    
    comparator - a Comparator to compare the elements
    
    Returns:
    
    a Collector which finds all the maximal elements and collects them to the List.
    
    See Also:
    
    maxAll(Comparator, Collector), maxAll()
  - maxAll
```
public static <T extends Comparable<? super T>,A,D> Collector<T,?,D> maxAll(Collector<T,A,D> downstream)
```
    Returns a Collector which finds all the elements which are equal to each other and bigger than any other element according to the natural order. The found elements are reduced using the specified downstream Collector.
    
    Type Parameters:
    
    T - the type of the input elements
    
    A - the intermediate accumulation type of the downstream collector
    
    D - the result type of the downstream reduction
    
    Parameters:
    
    downstream - a Collector implementing the downstream reduction
    
    Returns:
    
    a Collector which finds all the maximal elements.
    
    See Also:
    
    maxAll(Comparator, Collector), maxAll(Comparator), maxAll()
  - maxAll
```
public static <T extends Comparable<? super T>> Collector<T,?,List<T>> maxAll()
```
    Returns a Collector which finds all the elements which are equal to each other and bigger than any other element according to the natural order. The found elements are collected to List.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Returns:
    
    a Collector which finds all the maximal elements and collects them to the List.
    
    See Also:
    
    maxAll(Comparator), maxAll(Collector)
  - minAll
```
public static <T,A,D> Collector<T,?,D> minAll(Comparator<? super T> comparator,
                                              Collector<T,A,D> downstream)
```
    Returns a Collector which finds all the elements which are equal to each other and smaller than any other element according to the specified Comparator. The found elements are reduced using the specified downstream Collector.
    
    Type Parameters:
    
    T - the type of the input elements
    
    A - the intermediate accumulation type of the downstream collector
    
    D - the result type of the downstream reduction
    
    Parameters:
    
    comparator - a Comparator to compare the elements
    
    downstream - a Collector implementing the downstream reduction
    
    Returns:
    
    a Collector which finds all the minimal elements.
    
    See Also:
    
    minAll(Comparator), minAll(Collector), minAll()
  - minAll
```
public static <T> Collector<T,?,List<T>> minAll(Comparator<? super T> comparator)
```
    Returns a Collector which finds all the elements which are equal to each other and smaller than any other element according to the specified Comparator. The found elements are collected to List.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Parameters:
    
    comparator - a Comparator to compare the elements
    
    Returns:
    
    a Collector which finds all the minimal elements and collects them to the List.
    
    See Also:
    
    minAll(Comparator, Collector), minAll()
  - minAll
```
public static <T extends Comparable<? super T>,A,D> Collector<T,?,D> minAll(Collector<T,A,D> downstream)
```
    Returns a Collector which finds all the elements which are equal to each other and smaller than any other element according to the natural order. The found elements are reduced using the specified downstream Collector.
    
    Type Parameters:
    
    T - the type of the input elements
    
    A - the intermediate accumulation type of the downstream collector
    
    D - the result type of the downstream reduction
    
    Parameters:
    
    downstream - a Collector implementing the downstream reduction
    
    Returns:
    
    a Collector which finds all the minimal elements.
    
    See Also:
    
    minAll(Comparator, Collector), minAll(Comparator), minAll()
  - minAll
```
public static <T extends Comparable<? super T>> Collector<T,?,List<T>> minAll()
```
    Returns a Collector which finds all the elements which are equal to each other and smaller than any other element according to the natural order. The found elements are collected to List.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Returns:
    
    a Collector which finds all the minimal elements and collects them to the List.
    
    See Also:
    
    minAll(Comparator), minAll(Collector)
  - onlyOne
```
public static <T> Collector<T,?,Optional<T>> onlyOne()
```
    Returns a Collector which collects the stream element if stream contains exactly one element.
    This method returns a short-circuiting collector.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Returns:
    
    a collector which returns an Optional describing the only element of the stream. For empty stream or stream containing more than one element an empty Optional is returned.
    
    Since:
    
    0.4.0
  - first
```
public static <T> Collector<T,?,Optional<T>> first()
```
    Returns a Collector which collects only the first stream element if any.
    This method returns a short-circuiting collector.
    The operation performed by the returned collector is equivalent to stream.findFirst(). This collector is mostly useful as a downstream collector.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Returns:
    
    a collector which returns an Optional which describes the first element of the stream. For empty stream an empty Optional is returned.
  - last
```
public static <T> Collector<T,?,Optional<T>> last()
```
    Returns a Collector which collects only the last stream element if any.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Returns:
    
    a collector which returns an Optional which describes the last element of the stream. For empty stream an empty Optional is returned.
  - head
```
public static <T> Collector<T,?,List<T>> head(int n)
```
    Returns a Collector which collects at most specified number of the first stream elements into the List.
    This method returns a short-circuiting collector.
    There are no guarantees on the type, mutability, serializability, or thread-safety of the List returned.
    The operation performed by the returned collector is equivalent to stream.limit(n).collect(Collectors.toList()). This collector is mostly useful as a downstream collector.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Parameters:
    
    n - maximum number of stream elements to preserve
    
    Returns:
    
    a collector which returns a List containing the first n stream elements or less if the stream was shorter.
  - tail
```
public static <T> Collector<T,?,List<T>> tail(int n)
```
    Returns a Collector which collects at most specified number of the last stream elements into the List.
    There are no guarantees on the type, mutability, serializability, or thread-safety of the List returned.
    When supplied n is less or equal to zero, this method returns a short-circuiting collector which ignores the input and produces an empty list.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Parameters:
    
    n - maximum number of stream elements to preserve
    
    Returns:
    
    a collector which returns a List containing the last n stream elements or less if the stream was shorter.
  - greatest
```
public static <T> Collector<T,?,List<T>> greatest(Comparator<? super T> comparator,
                                                  int n)
```
    Returns a Collector which collects at most specified number of the greatest stream elements according to the specified Comparator into the List. The resulting List is sorted in comparator reverse order (greatest element is the first). The order of equal elements is the same as in the input stream.
    The operation performed by the returned collector is equivalent to stream.sorted(comparator.reversed()).limit(n).collect(Collectors.toList()) , but usually performed much faster if n is much less than the stream size.
    There are no guarantees on the type, mutability, serializability, or thread-safety of the List returned.
    When supplied n is less or equal to zero, this method returns a short-circuiting collector which ignores the input and produces an empty list.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Parameters:
    
    comparator - the comparator to compare the elements by
    
    n - maximum number of stream elements to preserve
    
    Returns:
    
    a collector which returns a List containing the greatest n stream elements or less if the stream was shorter.
  - greatest
```
public static <T extends Comparable<? super T>> Collector<T,?,List<T>> greatest(int n)
```
    Returns a Collector which collects at most specified number of the greatest stream elements according to the natural order into the List. The resulting List is sorted in reverse order (greatest element is the first). The order of equal elements is the same as in the input stream.
    The operation performed by the returned collector is equivalent to stream.sorted(Comparator.reverseOrder()).limit(n).collect(Collectors.toList()) , but usually performed much faster if n is much less than the stream size.
    There are no guarantees on the type, mutability, serializability, or thread-safety of the List returned.
    When supplied n is less or equal to zero, this method returns a short-circuiting collector which ignores the input and produces an empty list.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Parameters:
    
    n - maximum number of stream elements to preserve
    
    Returns:
    
    a collector which returns a List containing the greatest n stream elements or less if the stream was shorter.
  - least
```
public static <T> Collector<T,?,List<T>> least(Comparator<? super T> comparator,
                                               int n)
```
    Returns a Collector which collects at most specified number of the least stream elements according to the specified Comparator into the List. The resulting List is sorted in comparator order (least element is the first). The order of equal elements is the same as in the input stream.
    The operation performed by the returned collector is equivalent to stream.sorted(comparator).limit(n).collect(Collectors.toList()), but usually performed much faster if n is much less than the stream size.
    There are no guarantees on the type, mutability, serializability, or thread-safety of the List returned.
    When supplied n is less or equal to zero, this method returns a short-circuiting collector which ignores the input and produces an empty list.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Parameters:
    
    comparator - the comparator to compare the elements by
    
    n - maximum number of stream elements to preserve
    
    Returns:
    
    a collector which returns a List containing the least n stream elements or less if the stream was shorter.
  - least
```
public static <T extends Comparable<? super T>> Collector<T,?,List<T>> least(int n)
```
    Returns a Collector which collects at most specified number of the least stream elements according to the natural order into the List. The resulting List is sorted in natural order (least element is the first). The order of equal elements is the same as in the input stream.
    The operation performed by the returned collector is equivalent to stream.sorted().limit(n).collect(Collectors.toList()), but usually performed much faster if n is much less than the stream size.
    There are no guarantees on the type, mutability, serializability, or thread-safety of the List returned.
    When supplied n is less or equal to zero, this method returns a short-circuiting collector which ignores the input and produces an empty list.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Parameters:
    
    n - maximum number of stream elements to preserve
    
    Returns:
    
    a collector which returns a List containing the least n stream elements or less if the stream was shorter.
  - minIndex
```
public static <T> Collector<T,?,OptionalLong> minIndex(Comparator<? super T> comparator)
```
    Returns a Collector which finds the index of the minimal stream element according to the specified Comparator. If there are several minimal elements, the index of the first one is returned.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Parameters:
    
    comparator - a Comparator to compare the elements
    
    Returns:
    
    a Collector which finds the index of the minimal element.
    
    Since:
    
    0.3.5
    
    See Also:
    
    minIndex()
  - minIndex
```
public static <T extends Comparable<? super T>> Collector<T,?,OptionalLong> minIndex()
```
    Returns a Collector which finds the index of the minimal stream element according to the elements natural order. If there are several minimal elements, the index of the first one is returned.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Returns:
    
    a Collector which finds the index of the minimal element.
    
    Since:
    
    0.3.5
    
    See Also:
    
    minIndex(Comparator)
  - maxIndex
```
public static <T> Collector<T,?,OptionalLong> maxIndex(Comparator<? super T> comparator)
```
    Returns a Collector which finds the index of the maximal stream element according to the specified Comparator. If there are several maximal elements, the index of the first one is returned.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Parameters:
    
    comparator - a Comparator to compare the elements
    
    Returns:
    
    a Collector which finds the index of the maximal element.
    
    Since:
    
    0.3.5
    
    See Also:
    
    maxIndex()
  - maxIndex
```
public static <T extends Comparable<? super T>> Collector<T,?,OptionalLong> maxIndex()
```
    Returns a Collector which finds the index of the maximal stream element according to the elements natural order. If there are several maximal elements, the index of the first one is returned.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Returns:
    
    a Collector which finds the index of the maximal element.
    
    Since:
    
    0.3.5
    
    See Also:
    
    maxIndex(Comparator)
  - groupingByEnum
```
public static <T,K extends Enum<K>,A,D> Collector<T,?,EnumMap<K,D>> groupingByEnum(Class<K> enumClass,
                                                                                   Function<? super T,K> classifier,
                                                                                   Collector<? super T,A,D> downstream)
```
    Returns a Collector implementing a cascaded "group by" operation on input elements of type T, for classification function which maps input elements to the enum values. The downstream reduction for repeating keys is performed using the specified downstream Collector.
    Unlike the Collectors.groupingBy(Function, Collector) collector this collector produces an EnumMap which contains all possible keys including keys which were never returned by the classification function. These keys are mapped to the default collector value which is equivalent to collecting an empty stream with the same collector.
    This method returns a short-circuiting collector if the downstream collector is short-circuiting. The collection might stop when for every possible enum key the downstream collection is known to be finished.
    
    Type Parameters:
    
    T - the type of the input elements
    
    K - the type of the enum values returned by the classifier
    
    A - the intermediate accumulation type of the downstream collector
    
    D - the result type of the downstream reduction
    
    Parameters:
    
    enumClass - the class of enum values returned by the classifier
    
    classifier - a classifier function mapping input elements to enum values
    
    downstream - a Collector implementing the downstream reduction
    
    Returns:
    
    a Collector implementing the cascaded group-by operation
    
    Since:
    
    0.3.7
    
    See Also:
    
    Collectors.groupingBy(Function, Collector), groupingBy(Function, Set, Supplier, Collector)
  - groupingBy
```
public static <T,K,D,A> Collector<T,?,Map<K,D>> groupingBy(Function<? super T,? extends K> classifier,
                                                           Set<K> domain,
                                                           Collector<? super T,A,D> downstream)
```
    Returns a Collector implementing a cascaded "group by" operation on input elements of type T, grouping elements according to a classification function, and then performing a reduction operation on the values associated with a given key using the specified downstream Collector.
    There are no guarantees on the type, mutability, serializability, or thread-safety of the Map returned.
    The main difference of this collector from Collectors.groupingBy(Function, Collector) is that it accepts additional domain parameter which is the Set of all possible map keys. If the mapper function produces the key out of domain, an IllegalStateException will occur. If the mapper function does not produce some of domain keys at all, they are also added to the result. These keys are mapped to the default collector value which is equivalent to collecting an empty stream with the same collector.
    This method returns a short-circuiting collector if the downstream collector is short-circuiting. The collection might stop when for every possible key from the domain the downstream collection is known to be finished.
    
    Type Parameters:
    
    T - the type of the input elements
    
    K - the type of the keys
    
    A - the intermediate accumulation type of the downstream collector
    
    D - the result type of the downstream reduction
    
    Parameters:
    
    classifier - a classifier function mapping input elements to keys
    
    domain - a domain of all possible key values
    
    downstream - a Collector implementing the downstream reduction
    
    Returns:
    
    a Collector implementing the cascaded group-by operation with given domain
    
    Since:
    
    0.4.0
    
    See Also:
    
    groupingBy(Function, Set, Supplier, Collector), groupingByEnum(Class, Function, Collector)
  - groupingBy
```
public static <T,K,D,A,M extends Map<K,D>> Collector<T,?,M> groupingBy(Function<? super T,? extends K> classifier,
                                                                       Set<K> domain,
                                                                       Supplier<M> mapFactory,
                                                                       Collector<? super T,A,D> downstream)
```
    Returns a Collector implementing a cascaded "group by" operation on input elements of type T, grouping elements according to a classification function, and then performing a reduction operation on the values associated with a given key using the specified downstream Collector. The Map produced by the Collector is created with the supplied factory function.
    The main difference of this collector from Collectors.groupingBy(Function, Supplier, Collector) is that it accepts additional domain parameter which is the Set of all possible map keys. If the mapper function produces the key out of domain, an IllegalStateException will occur. If the mapper function does not produce some of domain keys at all, they are also added to the result. These keys are mapped to the default collector value which is equivalent to collecting an empty stream with the same collector.
    This method returns a short-circuiting collector if the downstream collector is short-circuiting. The collection might stop when for every possible key from the domain the downstream collection is known to be finished.
    
    Type Parameters:
    
    T - the type of the input elements
    
    K - the type of the keys
    
    A - the intermediate accumulation type of the downstream collector
    
    D - the result type of the downstream reduction
    
    M - the type of the resulting Map
    
    Parameters:
    
    classifier - a classifier function mapping input elements to keys
    
    domain - a domain of all possible key values
    
    downstream - a Collector implementing the downstream reduction
    
    mapFactory - a function which, when called, produces a new empty Map of the desired type
    
    Returns:
    
    a Collector implementing the cascaded group-by operation with given domain
    
    Since:
    
    0.4.0
    
    See Also:
    
    groupingBy(Function, Set, Collector), groupingByEnum(Class, Function, Collector)
  - intersecting
```
public static <T,S extends Collection<T>> Collector<S,?,Set<T>> intersecting()
```
    Returns a Collector which collects the intersection of the input collections into the newly-created Set.
    The returned collector produces an empty set if the input is empty or intersection of the input collections is empty.
    There are no guarantees on the type, mutability, serializability, or thread-safety of the Set returned.
    This method returns a short-circuiting collector: it may not process all the elements if the resulting intersection is empty.
    
    Type Parameters:
    
    T - the type of the elements in the input collections
    
    S - the type of the input collections
    
    Returns:
    
    a Collector which finds all the minimal elements and collects them to the List.
    
    Since:
    
    0.4.0
  - collectingAndThen
```
public static <T,A,R,RR> Collector<T,A,RR> collectingAndThen(Collector<T,A,R> downstream,
                                                             Function<R,RR> finisher)
```
    Adapts a Collector to perform an additional finishing transformation.
    Unlike Collectors.collectingAndThen(Collector, Function) this method returns a short-circuiting collector if the downstream collector is short-circuiting.
    
    Type Parameters:
    
    T - the type of the input elements
    
    A - intermediate accumulation type of the downstream collector
    
    R - result type of the downstream collector
    
    RR - result type of the resulting collector
    
    Parameters:
    
    downstream - a collector
    
    finisher - a function to be applied to the final result of the downstream collector
    
    Returns:
    
    a collector which performs the action of the downstream collector, followed by an additional finishing step
    
    Since:
    
    0.4.0
    
    See Also:
    
    Collectors.collectingAndThen(Collector, Function)
  - partitioningBy
```
public static <T,D,A> Collector<T,?,Map<Boolean,D>> partitioningBy(Predicate<? super T> predicate,
                                                                   Collector<? super T,A,D> downstream)
```
    Returns a Collector which partitions the input elements according to a Predicate, reduces the values in each partition according to another Collector, and organizes them into a Map<Boolean, D> whose values are the result of the downstream reduction.
    Unlike Collectors.partitioningBy(Predicate, Collector) this method returns a short-circuiting collector if the downstream collector is short-circuiting.
    
    Type Parameters:
    
    T - the type of the input elements
    
    A - the intermediate accumulation type of the downstream collector
    
    D - the result type of the downstream reduction
    
    Parameters:
    
    predicate - a predicate used for classifying input elements
    
    downstream - a Collector implementing the downstream reduction
    
    Returns:
    
    a Collector implementing the cascaded partitioning operation
    
    Since:
    
    0.4.0
    
    See Also:
    
    Collectors.partitioningBy(Predicate, Collector)
  - mapping
```
public static <T,U,A,R> Collector<T,?,R> mapping(Function<? super T,? extends U> mapper,
                                                 Collector<? super U,A,R> downstream)
```
    Adapts a Collector accepting elements of type U to one accepting elements of type T by applying a mapping function to each input element before accumulation.
    Unlike Collectors.mapping(Function, Collector) this method returns a short-circuiting collector if the downstream collector is short-circuiting.
    
    Type Parameters:
    
    T - the type of the input elements
    
    U - type of elements accepted by downstream collector
    
    A - intermediate accumulation type of the downstream collector
    
    R - result type of collector
    
    Parameters:
    
    mapper - a function to be applied to the input elements
    
    downstream - a collector which will accept mapped values
    
    Returns:
    
    a collector which applies the mapping function to the input elements and provides the mapped results to the downstream collector
    
    Since:
    
    0.4.0
    
    See Also:
    
    Collectors.mapping(Function, Collector)
  - mapping
```
public static <T,U> Collector<T,?,List<U>> mapping(Function<? super T,? extends U> mapper)
```
    Returns a collector which collects input elements to the new List transforming them with the supplied function beforehand.
    This method behaves like Collectors.mapping(mapper, Collectors.toList()).
    There are no guarantees on the type, mutability, serializability, or thread-safety of the List returned.
    
    Type Parameters:
    
    T - the type of the input elements
    
    U - the resulting type of the mapper function
    
    Parameters:
    
    mapper - a function to be applied to the input elements
    
    Returns:
    
    a collector which applies the mapping function to the input elements and collects the mapped results to the List
    
    Since:
    
    0.6.0
    
    See Also:
    
    mapping(Function, Collector)
  - flatMapping
```
public static <T,U,A,R> Collector<T,?,R> flatMapping(Function<? super T,? extends Stream<? extends U>> mapper,
                                                     Collector<? super U,A,R> downstream)
```
    Adapts a Collector accepting elements of type U to one accepting elements of type T by applying a flat mapping function to each input element before accumulation. The flat mapping function maps an input element to a stream covering zero or more output elements that are then accumulated downstream. Each mapped stream is closed after its contents have been placed downstream. (If a mapped stream is null an empty stream is used, instead.)
    This method is similar to Collectors.flatMapping method which appears in JDK 9. However when downstream collector is short-circuiting , this method will also return a short-circuiting collector.
    
    Type Parameters:
    
    T - the type of the input elements
    
    U - type of elements accepted by downstream collector
    
    A - intermediate accumulation type of the downstream collector
    
    R - result type of collector
    
    Parameters:
    
    mapper - a function to be applied to the input elements, which returns a stream of results
    
    downstream - a collector which will receive the elements of the stream returned by mapper
    
    Returns:
    
    a collector which applies the mapping function to the input elements and provides the flat mapped results to the downstream collector
    
    Since:
    
    0.4.1
  - flatMapping
```
public static <T,U> Collector<T,?,List<U>> flatMapping(Function<? super T,? extends Stream<? extends U>> mapper)
```
    Returns a collector which launches a flat mapping function for each input element and collects the elements of the resulting streams to the flat List. Each mapped stream is closed after its contents have been placed downstream. (If a mapped stream is null an empty stream is used, instead.)
    This method behaves like flatMapping(mapper, Collectors.toList()) .
    There are no guarantees on the type, mutability, serializability, or thread-safety of the List returned.
    
    Type Parameters:
    
    T - the type of the input elements
    
    U - type of the resulting elements
    
    Parameters:
    
    mapper - a function to be applied to the input elements, which returns a stream of results
    
    Returns:
    
    a collector which applies the mapping function to the input elements and collects the flat mapped results to the List
    
    Since:
    
    0.6.0
  - filtering
```
public static <T,A,R> Collector<T,?,R> filtering(Predicate<? super T> predicate,
                                                 Collector<T,A,R> downstream)
```
    Returns a Collector which passes only those elements to the specified downstream collector which match given predicate.
    This method returns a short-circuiting collector if downstream collector is short-circuiting.
    The operation performed by the returned collector is equivalent to stream.filter(predicate).collect(downstream). This collector is mostly useful as a downstream collector in cascaded operation involving pairing(Collector, Collector, BiFunction) collector.
    This method is similar to Collectors.filtering method which appears in JDK 9. However when downstream collector is short-circuiting , this method will also return a short-circuiting collector.
    
    Type Parameters:
    
    T - the type of the input elements
    
    A - intermediate accumulation type of the downstream collector
    
    R - result type of collector
    
    Parameters:
    
    predicate - a filter function to be applied to the input elements
    
    downstream - a collector which will accept filtered values
    
    Returns:
    
    a collector which applies the predicate to the input elements and provides the elements for which predicate returned true to the downstream collector
    
    Since:
    
    0.4.0
    
    See Also:
    
    pairing(Collector, Collector, BiFunction)
  - filtering
```
public static <T> Collector<T,?,List<T>> filtering(Predicate<? super T> predicate)
```
    Returns a Collector which filters input elements by the supplied predicate, collecting them to the list.
    This method behaves like filtering(predicate, Collectors.toList()).
    There are no guarantees on the type, mutability, serializability, or thread-safety of the List returned.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Parameters:
    
    predicate - a filter function to be applied to the input elements
    
    Returns:
    
    a collector which applies the predicate to the input elements and collects the elements for which predicate returned true to the List
    
    Since:
    
    0.6.0
    
    See Also:
    
    filtering(Predicate, Collector)
  - andingInt
```
public static <T> Collector<T,?,OptionalInt> andingInt(ToIntFunction<T> mapper)
```
    Returns a Collector which performs the bitwise-and operation of a integer-valued function applied to the input elements. If no elements are present, the result is empty OptionalInt.
    This method returns a short-circuiting collector: it may not process all the elements if the result is zero.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Parameters:
    
    mapper - a function extracting the property to be processed
    
    Returns:
    
    a Collector that produces the bitwise-and operation of a derived property
    
    Since:
    
    0.4.0
  - andingLong
```
public static <T> Collector<T,?,OptionalLong> andingLong(ToLongFunction<T> mapper)
```
    Returns a Collector which performs the bitwise-and operation of a long-valued function applied to the input elements. If no elements are present, the result is empty OptionalLong.
    This method returns a short-circuiting collector: it may not process all the elements if the result is zero.
    
    Type Parameters:
    
    T - the type of the input elements
    
    Parameters:
    
    mapper - a function extracting the property to be processed
    
    Returns:
    
    a Collector that produces the bitwise-and operation of a derived property
    
    Since:
    
    0.4.0
  - commonPrefix
```
public static Collector<CharSequence,?,String> commonPrefix()
```
    Returns a Collector which computes a common prefix of input CharSequence objects returning the result as String. For empty input the empty String is returned.
    The returned Collector handles specially Unicode surrogate pairs: the returned prefix may end with Unicode high-surrogate code unit only if it's not succeeded by Unicode low-surrogate code unit in any of the input sequences. Normally the ending high-surrogate code unit is removed from the prefix.
    This method returns a short-circuiting collector: it may not process all the elements if the common prefix is empty.
    
    Returns:
    
    a Collector which computes a common prefix.
    
    Since:
    
    0.5.0
  - commonSuffix
```
public static Collector<CharSequence,?,String> commonSuffix()
```
    Returns a Collector which computes a common suffix of input CharSequence objects returning the result as String. For empty input the empty String is returned.
    The returned Collector handles specially Unicode surrogate pairs: the returned suffix may start with Unicode low-surrogate code unit only if it's not preceded by Unicode high-surrogate code unit in any of the input sequences. Normally the starting low-surrogate code unit is removed from the suffix.
    This method returns a short-circuiting collector: it may not process all the elements if the common suffix is empty.
    
    Returns:
    
    a Collector which computes a common suffix.
    
    Since:
    
    0.5.0
  - dominators
```
public static <T> Collector<T,?,List<T>> dominators(BiPredicate<? super T,? super T> isDominator)
```
    Returns a collector which collects input elements into List removing the elements following their dominator element. The dominator elements are defined according to given isDominator BiPredicate. The isDominator relation must be transitive (if A dominates over B and B dominates over C, then A also dominates over C).
    This operation is similar to streamEx.collapse(isDominator).toList(). The important difference is that in this method BiPredicate accepts not the adjacent stream elements, but the leftmost element of the series (current dominator) and the current element.
    For example, consider the stream of numbers:
```
 StreamEx<Integer> stream = StreamEx.of(1, 5, 3, 4, 2, 7);
 
```
    Using stream.collapse((a, b) -> a >= b).toList() you will get the numbers which are bigger than their immediate predecessor ( [1, 5, 4, 7]), because (3, 4) pair is not collapsed. However using stream.collect(dominators((a, b) -> a >= b)) you will get the numbers which are bigger than any predecessor ([1, 5, 7]) as 5 is the dominator element for the subsequent 3, 4 and 2.
    Type Parameters:
    
    T - type of the input elements.
    
    Parameters:
    
    isDominator - a non-interfering, stateless, transitive BiPredicate which returns true if the first argument is the dominator for the second argument.
    
    Returns:
    
    a collector which collects input element into List leaving only dominator elements.
    
    Since:
    
    0.5.1
    
    See Also:
    
    StreamEx.collapse(BiPredicate)
  - ifAllMatch
```
public static <T,A,R> Collector<T,?,Optional<R>> ifAllMatch(Predicate<T> predicate,
                                                            Collector<T,A,R> downstream)
```
    Returns a Collector which performs downstream reduction if all elements satisfy the Predicate. The result is described as an Optional<R>.
    The resulting collector returns an empty optional if at least one input element does not satisfy the predicate. Otherwise it returns an optional which contains the result of the downstream collector.
    This method returns a short-circuiting collector: it may not process all the elements if some of items don't satisfy the predicate or if downstream collector is a short-circuiting collector.
    It's guaranteed that the downstream collector is not called for elements which don't satisfy the predicate.
    
    Type Parameters:
    
    T - the type of input elements
    
    A - intermediate accumulation type of the downstream collector
    
    R - result type of the downstream collector
    
    Parameters:
    
    predicate - a non-interfering, stateless predicate to checks whether collector should proceed with element
    
    downstream - a Collector implementing the downstream reduction
    
    Returns:
    
    a Collector witch performs downstream reduction if all elements satisfy the predicate
    
    See Also:
    
    Stream.allMatch(Predicate), AbstractStreamEx.dropWhile(Predicate), AbstractStreamEx.takeWhile(Predicate)

Class MoreCollectors

Method Summary

Methods inherited from class Object

Method Detail

toArray

toBooleanArray

toEnumSet

distinctCount

distinctBy

countingInt

pairing

minMax

maxAll

maxAll

maxAll

maxAll

minAll

minAll

minAll

minAll

onlyOne

first

last

head

tail

greatest

greatest

least

least

minIndex

minIndex

maxIndex

maxIndex

groupingByEnum

groupingBy

groupingBy

intersecting

collectingAndThen

partitioningBy

mapping

mapping

flatMapping

flatMapping

filtering

filtering

andingInt

andingLong

commonPrefix

commonSuffix

dominators

ifAllMatch