# Package-level declarations

Sequence type that represents lazily evaluated collections. Top-level functions for instantiating sequences and extension functions for sequences.

## Classification of sequences

The sequence operations can be classified into the following groups regarding their state requirements:

*stateless*– operations which require no state and process each element independently like kotlin.sequences.Sequence.map, kotlin.sequences.Sequence.filter, or require a small constant amount of state to process an element, for example kotlin.sequences.Sequence.take or kotlin.sequences.Sequence.drop;*stateful*– operations which require a significant amount of state, usually proportional to the number of elements in a sequence.

If the sequence operation returns another sequence, which is produced lazily, it's called *intermediate*, and otherwise the operation is *terminal*. Examples of terminal operations are kotlin.sequences.Sequence.toList, kotlin.sequences.Sequence.max.

Sequences can be iterated multiple times, however some sequence implementations might constrain themselves to be iterated only once. That is mentioned specifically in their documentation (e.g. kotlin.sequences.generateSequence overload). The latter sequences throw an exception on an attempt to iterate them the second time.

Sequence type that represents lazily evaluated collections. Top-level functions for instantiating sequences and extension functions for sequences.

## Classification of sequences

The sequence operations can be classified into the following groups regarding their state requirements:

*stateless*– operations which require no state and process each element independently like kotlin.sequences.Sequence.map, kotlin.sequences.Sequence.filter, or require a small constant amount of state to process an element, for example kotlin.sequences.Sequence.take or kotlin.sequences.Sequence.drop;*stateful*– operations which require a significant amount of state, usually proportional to the number of elements in a sequence.

If the sequence operation returns another sequence, which is produced lazily, it's called *intermediate*, and otherwise the operation is *terminal*. Examples of terminal operations are kotlin.sequences.Sequence.toList, kotlin.sequences.Sequence.max.

Sequences can be iterated multiple times, however some sequence implementations might constrain themselves to be iterated only once. That is mentioned specifically in their documentation (e.g. kotlin.sequences.generateSequence overload). The latter sequences throw an exception on an attempt to iterate them the second time.

## Functions

Creates a sequence that returns all elements from this iterator. The sequence is constrained to be iterated only once.

**Since Kotlin**1.0

Returns this sequence as a Sequence.

**Since Kotlin**1.0

Creates a sequence that returns all values from this enumeration. The sequence is constrained to be iterated only once.

**Since Kotlin**1.0

Returns a Map containing the elements from the given sequence indexed by the key returned from keySelector function applied to each element.

**Since Kotlin**1.0

Returns a Map containing the values provided by valueTransform and indexed by keySelector functions applied to elements of the given sequence.

**Since Kotlin**1.0

Populates and returns the destination mutable map with key-value pairs, where key is provided by the keySelector function applied to each element of the given sequence and value is the element itself.

**Since Kotlin**1.0

Populates and returns the destination mutable map with key-value pairs, where key is provided by the keySelector function and and value is provided by the valueTransform function applied to elements of the given sequence.

**Since Kotlin**1.0

Populates and returns the destination mutable map with key-value pairs for each element of the given sequence, where key is the element itself and value is provided by the valueSelector function applied to that key.

**Since Kotlin**1.3

Returns an average value of elements in the sequence.

**Since Kotlin**1.0

Appends all elements matching the given predicate to the given destination.

**Since Kotlin**1.0

Returns a sequence containing all elements that are instances of specified type parameter R.

**Since Kotlin**1.0

Appends all elements that are instances of specified type parameter R to the given destination.

**Since Kotlin**1.0

Appends all elements that are instances of specified class to the given destination.

**Since Kotlin**1.0

Appends all elements that are not `null`

to the given destination.

**Since Kotlin**1.0

Appends all elements not matching the given predicate to the given destination.

**Since Kotlin**1.0

Returns a single sequence of all elements from results of transform function being invoked on each element of original sequence.

**Since Kotlin**1.4

Returns a single sequence of all elements from results of transform function being invoked on each element of original sequence.

**Since Kotlin**1.0

Returns a single sequence of all elements yielded from results of transform function being invoked on each element and its index in the original sequence.

**Since Kotlin**1.4

Appends all elements yielded from results of transform function being invoked on each element and its index in the original sequence, to the given destination.

**Since Kotlin**1.4

Appends all elements yielded from results of transform function being invoked on each element of original sequence, to the given destination.

**Since Kotlin**1.4

Appends all elements yielded from results of transform function being invoked on each element of original sequence, to the given destination.

**Since Kotlin**1.0

Returns a sequence of all elements from all iterables in this sequence.

**Since Kotlin**1.0

Returns a sequence of all elements from all sequences in this sequence.

**Since Kotlin**1.0

Returns a sequence which invokes the function to calculate the next value on each iteration until the function returns `null`

.

**Since Kotlin**1.0

Returns a sequence defined by the starting value seed and the function nextFunction, which is invoked to calculate the next value based on the previous one on each iteration.

**Since Kotlin**1.0

Returns a sequence defined by the function seedFunction, which is invoked to produce the starting value, and the nextFunction, which is invoked to calculate the next value based on the previous one on each iteration.

**Since Kotlin**1.0

Groups elements of the original sequence by the key returned by the given keySelector function applied to each element and returns a map where each group key is associated with a list of corresponding elements.

**Since Kotlin**1.0

Groups values returned by the valueTransform function applied to each element of the original sequence by the key returned by the given keySelector function applied to the element and returns a map where each group key is associated with a list of corresponding values.

**Since Kotlin**1.0

Groups elements of the original sequence by the key returned by the given keySelector function applied to each element and puts to the destination map each group key associated with a list of corresponding elements.

**Since Kotlin**1.0

Groups values returned by the valueTransform function applied to each element of the original sequence by the key returned by the given keySelector function applied to the element and puts to the destination map each group key associated with a list of corresponding values.

**Since Kotlin**1.0

Appends the string from all the elements separated using separator and using the given prefix and postfix if supplied.

**Since Kotlin**1.0

Creates a string from all the elements separated using separator and using the given prefix and postfix if supplied.

**Since Kotlin**1.0

Applies the given transform function to each element and its index in the original sequence and appends only the non-null results to the given destination.

**Since Kotlin**1.0

Applies the given transform function to each element and its index in the original sequence and appends the results to the given destination.

**Since Kotlin**1.0

Applies the given transform function to each element in the original sequence and appends only the non-null results to the given destination.

**Since Kotlin**1.0

Returns the largest element.

**Since Kotlin**1.7

Returns the first element yielding the largest value of the given function or `null`

if there are no elements.

**Since Kotlin**1.4

Returns the largest value among all values produced by selector function applied to each element in the sequence.

**Since Kotlin**1.4

Returns the largest value among all values produced by selector function applied to each element in the sequence or `null`

if there are no elements.

**Since Kotlin**1.4

Returns the largest value according to the provided comparator among all values produced by selector function applied to each element in the sequence or `null`

if there are no elements.

**Since Kotlin**1.4

Returns the first element having the largest value according to the provided comparator or `null`

if there are no elements.

**Since Kotlin**1.4

Returns the smallest element.

**Since Kotlin**1.7

Returns the first element yielding the smallest value of the given function or `null`

if there are no elements.

**Since Kotlin**1.4

Returns the smallest value among all values produced by selector function applied to each element in the sequence.

**Since Kotlin**1.4

Returns the smallest value among all values produced by selector function applied to each element in the sequence or `null`

if there are no elements.

**Since Kotlin**1.4

Returns the smallest value according to the provided comparator among all values produced by selector function applied to each element in the sequence or `null`

if there are no elements.

**Since Kotlin**1.4

Returns a sequence containing all elements of the original sequence without the first occurrence of the given element.

**Since Kotlin**1.0

Returns a sequence containing all elements of original sequence except the elements contained in the given elements array.

**Since Kotlin**1.0

Returns a sequence containing all elements of original sequence except the elements contained in the given elements collection.

**Since Kotlin**1.0

Returns a sequence containing all elements of original sequence except the elements contained in the given elements sequence.

**Since Kotlin**1.0

Returns the first element having the smallest value according to the provided comparator or `null`

if there are no elements.

**Since Kotlin**1.4

Returns a sequence containing all elements of the original sequence and then the given element.

**Since Kotlin**1.0

Returns a sequence containing all elements of original sequence and then all elements of the given elements array.

**Since Kotlin**1.0

Returns a sequence containing all elements of original sequence and then all elements of the given elements collection.

**Since Kotlin**1.0

Returns a sequence containing all elements of original sequence and then all elements of the given elements sequence.

**Since Kotlin**1.0

Returns an original collection containing all the non-`null`

elements, throwing an IllegalArgumentException if there are any `null`

elements.

**Since Kotlin**1.0

Returns a sequence containing successive accumulation values generated by applying operation from left to right to each element, its index in the original sequence and current accumulator value that starts with initial value.

**Since Kotlin**1.4

Returns a sequence containing successive accumulation values generated by applying operation from left to right to each element and current accumulator value that starts with the first element of this sequence.

**Since Kotlin**1.4

Returns a sequence containing successive accumulation values generated by applying operation from left to right to each element, its index in the original sequence and current accumulator value that starts with the first element of this sequence.

**Since Kotlin**1.4

Returns a sequence containing successive accumulation values generated by applying operation from left to right to each element, its index in the original sequence and current accumulator value that starts with initial value.

**Since Kotlin**1.4

Creates a sequence that returns the specified values.

**Since Kotlin**1.0

Returns a sequence that yields elements of this sequence randomly shuffled.

**Since Kotlin**1.4

Returns a sequence that yields elements of this sequence randomly shuffled using the specified random instance as the source of randomness.

**Since Kotlin**1.4

Returns the single element, or throws an exception if the sequence is empty or has more than one element.

**Since Kotlin**1.0

Returns the single element matching the given predicate, or throws exception if there is no or more than one matching element.

**Since Kotlin**1.0

Returns single element, or `null`

if the sequence is empty or has more than one element.

**Since Kotlin**1.0

Returns the single element matching the given predicate, or `null`

if element was not found or more than one element was found.

**Since Kotlin**1.0

Returns a sequence that yields elements of this sequence sorted descending according to their natural sort order.

**Since Kotlin**1.0

Returns a sequence that yields elements of this sequence sorted according to the specified comparator.

**Since Kotlin**1.0

Returns the sum of all elements in the sequence.

**Since Kotlin**1.0

Returns the sum of all elements in the sequence.

**Since Kotlin**1.5

Returns the sum of all values produced by selector function applied to each element in the sequence.

**Since Kotlin**1.4

Returns the sum of all values produced by selector function applied to each element in the sequence.

**Since Kotlin**1.5

Returns the sum of all values produced by selector function applied to each element in the sequence.

**Since Kotlin**1.4

Appends all elements to the given destination collection.

**Since Kotlin**1.0

Returns a new MutableList filled with all elements of this sequence.

**Since Kotlin**1.0

Returns a new MutableSet containing all distinct elements from the given sequence.

**Since Kotlin**1.0

Returns a new SortedSet of all elements.

**Since Kotlin**1.0

Returns a sequence of snapshots of the window of the given size sliding along this sequence with the given step, where each snapshot is a list.

**Since Kotlin**1.2

Returns a sequence of results of applying the given transform function to an each list representing a view over the window of the given size sliding along this sequence with the given step.

**Since Kotlin**1.2

Returns a sequence that wraps each element of the original sequence into an IndexedValue containing the index of that element and the element itself.

**Since Kotlin**1.0

Returns a sequence of values built from the elements of `this`

sequence and the other sequence with the same index. The resulting sequence ends as soon as the shortest input sequence ends.

**Since Kotlin**1.0

Returns a sequence of values built from the elements of `this`

sequence and the other sequence with the same index using the provided transform function applied to each pair of elements. The resulting sequence ends as soon as the shortest input sequence ends.

**Since Kotlin**1.0

Returns a sequence of pairs of each two adjacent elements in this sequence.

**Since Kotlin**1.2

Returns a sequence containing the results of applying the given transform function to an each pair of two adjacent elements in this sequence.

**Since Kotlin**1.2

Since Kotlin1.0