Package com.gengoai.collection

Class Iterators

java.lang.Object

com.gengoai.collection.Iterators

public final class Iterators
extends Object

Methods for manipulating iterators

Author:

David B. Bracewell

Method Summary

Modifier and Type	Method	Description
static Iterator<?>	asIterator(Object object)	As iterator iterator.
static <T> Iterator<T>	concat(Iterable<? extends T>... iterables)	Concatenates iterables together
static <T> Iterator<T>	concat(Iterator<? extends T>... iterators)	Concatenates iterators together
static <E> Iterator<E>	filter(Iterator<? extends E> iterator, SerializablePredicate<? super E> filter)	Filters elements from the given iterator when the given filter predicate evaluates to false
static <T> Optional<T>	first(Iterator<? extends T> iterator)	Gets the first element of the iterator that would be returned by calling next if it exists.
static <T> T	first(Iterator<? extends T> iterator, T defaultValue)	Gets the first element of the iterator that would be returned by calling next if it exists or the default value.
static <T> Iterator<T>	flatten(Iterator<? extends Iterator<? extends T>> iterator)	Flattens an iterator of iterators.
static <T> Optional<T>	get(Iterator<? extends T> iterator, int n)	Gets the element of the iterator after iterator index times if it exists
static <T> T	get(Iterator<? extends T> iterator, int n, T defaultValue)	Gets the element of the iterator after iterator index times if it exists and if it does not exist, returns the default value
static <T> Optional<T>	last(Iterator<? extends T> iterator)	Gets the last element of the iterator that would be returned by calling next until hasNext returns false if it exists.
static <T> T	last(Iterator<? extends T> iterator, T defaultValue)	Gets the last element of the iterator that would be returned by calling next until hasNext returns false if it exists or the default value.
static <T> Optional<T>	next(Iterator<? extends T> iterator)	Gets the next element of the iterator that would be returned by calling next if it exists.
static <T> T	next(Iterator<? extends T> iterator, T defaultValue)	Gets the next element of the iterator that would be returned by calling next if it exists or the default value.
static <T> Iterator<List<T>>	partition(Iterator<? extends T> iterator, int partitionSize, boolean pad)	Partitions the elements in the iterator into a number of lists equal to partition size except for the last partition, which may have less elements if pad is false but will be filled with nulls if true.
static <T> Iterator<List<T>>	partition(Iterator<T> iterator, int partitionSize)	Partitions the elements in the iterator into a number of lists equal to partition size except for the last partition, which may have less elements.
static <T> Iterator<T>	singletonIterator(T object)
static int	size(Iterator<?> iterator)	Gets the number of items in the iterator
static <I,O> Iterator<O>	transform(Iterator<? extends I> iterator, SerializableFunction<? super I,? extends O> function)	Creates an iterator that transforms the elements of the iterator
static <T> Iterator<T>	unmodifiableIterator(Iterator<? extends T> iterator)	Wraps an iterator allowing items to not be removed
static <T,U> Iterator<Map.Entry<T,U>>	zip(Iterator<? extends T> iterator1, Iterator<? extends U> iterator2)	Zips (combines) two iterators together.
static <T> Iterator<Map.Entry<T,Integer>>	zipWithIndex(Iterator<? extends T> iterator)	Creates pairs of entries from the given iterator and its index in the iterator (0 based)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

asIterator

public static Iterator<?> asIterator(Object object)

As iterator iterator.

Parameters:

object - the object

Returns:

the iterator

concat

@SafeVarargs
public static <T> Iterator<T> concat(Iterator<? extends T>... iterators)

Concatenates iterators together

Type Parameters:

T - the iterator element type parameter

Parameters:

iterators - the iterators to concatenate

Returns:

the concatenated iterator

concat

@SafeVarargs
public static <T> Iterator<T> concat(Iterable<? extends T>... iterables)

Concatenates iterables together

Type Parameters:

T - the iterables element type parameter

Parameters:

iterables - the iterables to concatenate

Returns:

the concatenated iterator

filter

public static <E> Iterator<E> filter(Iterator<? extends E> iterator,
                                     SerializablePredicate<? super E> filter)

Filters elements from the given iterator when the given filter predicate evaluates to false

Type Parameters:

E - the iterator element parameter

Parameters:

iterator - the iterator to filter

filter - the filter to apply items evaluating to false will be removed from the iterator

Returns:

the filtered iterator

first

public static <T> T first(Iterator<? extends T> iterator,
                          T defaultValue)

Gets the first element of the iterator that would be returned by calling next if it exists or the default value.

Type Parameters:

T - the iterator element type parameter

Parameters:

iterator - the iterator

defaultValue - the default value

Returns:

the first element in the iterator or the default value

first

public static <T> Optional<T> first(Iterator<? extends T> iterator)

Gets the first element of the iterator that would be returned by calling next if it exists.

Type Parameters:

T - the iterator element type parameter

Parameters:

iterator - the iterator

Returns:

the first element in the iterator

flatten

public static <T> Iterator<T> flatten(Iterator<? extends Iterator<? extends T>> iterator)

Flattens an iterator of iterators.

Type Parameters:

T - the iterator element type parameter

Parameters:

iterator - the iterator

Returns:

the flattened iterator

get

public static <T> Optional<T> get(Iterator<? extends T> iterator,
                                  int n)

Gets the element of the iterator after iterator index times if it exists

Type Parameters:

T - the iterator element type parameter

Parameters:

iterator - the iterator

n - how many times to iterate

Returns:

Optional of the element of the iterator after iterating n times if it exists

get

public static <T> T get(Iterator<? extends T> iterator,
                        int n,
                        T defaultValue)

Gets the element of the iterator after iterator index times if it exists and if it does not exist, returns the default value

Type Parameters:

T - the iterator element type parameter

Parameters:

iterator - the iterator

n - how many times to iterate

defaultValue - the default value to return if nothing is at the given index

Returns:

the element of the iterator after iterating n times or default value if cannot iterator n times

last

public static <T> T last(Iterator<? extends T> iterator,
                         T defaultValue)

Gets the last element of the iterator that would be returned by calling next until hasNext returns false if it exists or the default value.

Type Parameters:

T - the iterator element type parameter

Parameters:

iterator - the iterator

defaultValue - the default value

Returns:

the last element in the iterator or the default value

last

public static <T> Optional<T> last(Iterator<? extends T> iterator)

Gets the last element of the iterator that would be returned by calling next until hasNext returns false if it exists.

Type Parameters:

T - the iterator element type parameter

Parameters:

iterator - the iterator

Returns:

the last element in the iterator

next

public static <T> Optional<T> next(Iterator<? extends T> iterator)

Gets the next element of the iterator that would be returned by calling next if it exists.

Type Parameters:

T - the iterator element type parameter

Parameters:

iterator - the iterator

Returns:

the next element in the iterator

next

public static <T> T next(Iterator<? extends T> iterator,
                         T defaultValue)

Gets the next element of the iterator that would be returned by calling next if it exists or the default value.

Type Parameters:

T - the iterator element type parameter

Parameters:

iterator - the iterator

defaultValue - the default value

Returns:

the next element in the iterator or the default value

partition

public static <T> Iterator<List<T>> partition(Iterator<T> iterator,
                                              int partitionSize)

Partitions the elements in the iterator into a number of lists equal to partition size except for the last partition, which may have less elements.

Type Parameters:

T - the iterator element type parameter

Parameters:

iterator - the iterator to partition

partitionSize - the partition size

Returns:

the partitioned iterator

partition

public static <T> Iterator<List<T>> partition(Iterator<? extends T> iterator,
                                              int partitionSize,
                                              boolean pad)

Partitions the elements in the iterator into a number of lists equal to partition size except for the last partition, which may have less elements if pad is false but will be filled with nulls if true.

Type Parameters:

T - the iterator element type parameter

Parameters:

iterator - the iterator to partition

partitionSize - the partition size

pad - true add nulls to ensure list size is equal to partition size

Returns:

the partitioned iterator

singletonIterator

public static <T> Iterator<T> singletonIterator(T object)

size

public static int size(Iterator<?> iterator)

Gets the number of items in the iterator

Parameters:

iterator - the iterator

Returns:

the size or number of items in the iterator

transform

public static <I,O> Iterator<O> transform(Iterator<? extends I> iterator,
                                                SerializableFunction<? super I,? extends O> function)

Creates an iterator that transforms the elements of the iterator

Type Parameters:

I - the type parameter of the item in given iterator

O - the type parameter of the output of the transform function

Parameters:

iterator - the iterator to transform

function - the transform function

Returns:

the transformed iterator

unmodifiableIterator

public static <T> Iterator<T> unmodifiableIterator(Iterator<? extends T> iterator)

Wraps an iterator allowing items to not be removed

Type Parameters:

T - the iterator element type parameter

Parameters:

iterator - the iterator to make unmodifiable

Returns:

the unmodifiable iterator

zip

public static <T,U> Iterator<Map.Entry<T,U>> zip(Iterator<? extends T> iterator1,
                                                             Iterator<? extends U> iterator2)

Zips (combines) two iterators together. For example, if iterator 1 contained [1,2,3] and iterator 2 contained [4,5,6] the result would be [(1,4), (2,5), (3,6)]. Note that the length of the resulting stream will be the minimum of the two iterators.

Type Parameters:

T - the component type of the first iterator

U - the component type of the second iterator

Parameters:

iterator1 - the iterator making up the key in the resulting entries

iterator2 - the iterator making up the value in the resulting entries

Returns:

A stream of entries whose keys are taken from iterator1 and values are taken from iterator2

zipWithIndex

public static <T> Iterator<Map.Entry<T,Integer>> zipWithIndex(Iterator<? extends T> iterator)

Creates pairs of entries from the given iterator and its index in the iterator (0 based)

Type Parameters:

T - the iterator type parameter

Parameters:

iterator - the iterator

Returns:

the iterator with index values