Instance Method

# first(where:)

Returns the first element of the sequence that satisfies the given predicate.

## Parameters

`predicate`

A closure that takes an element of the sequence as its argument and returns a Boolean value indicating whether the element is a match.

## Return Value

The first element of the sequence that satisfies `predicate`, or `nil` if there is no element that satisfies `predicate`.

## Discussion

The following example uses the `first(where:)` method to find the first negative number in an array of integers:

Complexity: O(n), where n is the length of the sequence.

### Combining Sequence Elements

`func allSatisfy((UInt8) -> Bool) -> Bool`

Returns a Boolean value indicating whether every element of a sequence satisfies a given predicate.

`func compactMap<ElementOfResult>((UInt8) -> ElementOfResult?) -> [ElementOfResult]`

Returns an array containing the non-`nil` results of calling the given transformation with each element of this sequence.

`func contains(UInt8) -> Bool`

Returns a Boolean value indicating whether the sequence contains the given element.

`func contains(where: (UInt8) -> Bool) -> Bool`

Returns a Boolean value indicating whether the sequence contains an element that satisfies the given predicate.

`func distance(from: Int, to: Int) -> Int`

Returns the distance between two indexes.

`func drop(while: (UInt8) -> Bool) -> Slice<DispatchData>`

Returns a subsequence by skipping elements while `predicate` returns `true` and returning the remaining elements.

`func dropFirst(Int) -> Slice<DispatchData>`

Returns a subsequence containing all but the given number of initial elements.

`func dropLast(Int) -> Slice<DispatchData>`

Returns a subsequence containing all but the specified number of final elements.

`func elementsEqual<OtherSequence>(OtherSequence) -> Bool`

Returns a Boolean value indicating whether this sequence and another sequence contain the same elements in the same order.

`func elementsEqual<OtherSequence>(OtherSequence, by: (UInt8, OtherSequence.Element) -> Bool) -> Bool`

Returns a Boolean value indicating whether this sequence and another sequence contain equivalent elements in the same order, using the given predicate as the equivalence test.

`func enumerated() -> EnumeratedSequence<DispatchData>`

Returns a sequence of pairs (n, x), where n represents a consecutive integer starting at zero and x represents an element of the sequence.

`func filter((UInt8) -> Bool) -> [UInt8]`

Returns an array containing, in order, the elements of the sequence that satisfy the given predicate.

`func firstIndex(of: UInt8) -> Int?`

Returns the first index where the specified value appears in the collection.

`func firstIndex(where: (UInt8) -> Bool) -> Int?`

Returns the first index in which an element of the collection satisfies the given predicate.

`func forEach((UInt8) -> Void)`

Calls the given closure on each element in the sequence in the same order as a `for`-`in` loop.

`func formIndex(inout Int, offsetBy: Int)`

Offsets the given index by the specified distance.

`func formIndex(inout Int, offsetBy: Int, limitedBy: Int) -> Bool`

Offsets the given index by the specified distance, or so that it equals the given limiting index.

`func formIndex(after: inout Int)`

Replaces the given index with its successor.

`func formIndex(before: inout Int)`

Replaces the given index with its predecessor.

`func index(Int, offsetBy: Int) -> Int`

Returns an index that is the specified distance from the given index.

`func index(Int, offsetBy: Int, limitedBy: Int) -> Int?`

Returns an index that is the specified distance from the given index, unless that distance is beyond a given limiting index.

`func last(where: (UInt8) -> Bool) -> UInt8?`

Returns the last element of the sequence that satisfies the given predicate.

`func lastIndex(of: UInt8) -> Int?`

Returns the last index where the specified value appears in the collection.

`func lastIndex(where: (UInt8) -> Bool) -> Int?`

Returns the index of the last element in the collection that matches the given predicate.

`func lexicographicallyPrecedes<OtherSequence>(OtherSequence) -> Bool`

Returns a Boolean value indicating whether the sequence precedes another sequence in a lexicographical (dictionary) ordering, using the less-than operator (`<`) to compare elements.

`func lexicographicallyPrecedes<OtherSequence>(OtherSequence, by: (UInt8, UInt8) -> Bool) -> Bool`

Returns a Boolean value indicating whether the sequence precedes another sequence in a lexicographical (dictionary) ordering, using the given predicate to compare elements.

`func map<T>((UInt8) -> T) -> [T]`

Returns an array containing the results of mapping the given closure over the sequence’s elements.

`func max() -> UInt8?`

Returns the maximum element in the sequence.

`func max(by: (UInt8, UInt8) -> Bool) -> UInt8?`

Returns the maximum element in the sequence, using the given predicate as the comparison between elements.

`func min() -> UInt8?`

Returns the minimum element in the sequence.

`func min(by: (UInt8, UInt8) -> Bool) -> UInt8?`

Returns the minimum element in the sequence, using the given predicate as the comparison between elements.

`func prefix(Int) -> Slice<DispatchData>`

Returns a subsequence, up to the specified maximum length, containing the initial elements of the collection.

`func prefix(through: Int) -> Slice<DispatchData>`

Returns a subsequence from the start of the collection through the specified position.

`func prefix(upTo: Int) -> Slice<DispatchData>`

Returns a subsequence from the start of the collection up to, but not including, the specified position.

`func prefix(while: (UInt8) -> Bool) -> Slice<DispatchData>`

Returns a subsequence containing the initial elements until `predicate` returns `false` and skipping the remaining elements.

`func randomElement() -> UInt8?`

Returns a random element of the collection.

`func randomElement<T>(using: inout T) -> UInt8?`

Returns a random element of the collection, using the given generator as a source for randomness.

`func reduce<Result>(Result, (Result, UInt8) -> Result) -> Result`

Returns the result of combining the elements of the sequence using the given closure.

`func reversed() -> ReversedCollection<DispatchData>`

Returns a view presenting the elements of the collection in reverse order.

`func shuffled() -> [UInt8]`

Returns the elements of the sequence, shuffled.

`func shuffled<T>(using: inout T) -> [UInt8]`

Returns the elements of the sequence, shuffled using the given generator as a source for randomness.

`func sorted() -> [UInt8]`

Returns the elements of the sequence, sorted.

`func sorted(by: (UInt8, UInt8) -> Bool) -> [UInt8]`

Returns the elements of the sequence, sorted using the given predicate as the comparison between elements.

`func split(maxSplits: Int, omittingEmptySubsequences: Bool, whereSeparator: (UInt8) -> Bool) -> [Slice<DispatchData>]`

Returns the longest possible subsequences of the collection, in order, that don’t contain elements satisfying the given predicate.

`func split(separator: UInt8, maxSplits: Int, omittingEmptySubsequences: Bool) -> [Slice<DispatchData>]`

Returns the longest possible subsequences of the collection, in order, around elements equal to the given element.

`func starts<PossiblePrefix>(with: PossiblePrefix) -> Bool`

Returns a Boolean value indicating whether the initial elements of the sequence are the same as the elements in another sequence.

`func starts<PossiblePrefix>(with: PossiblePrefix, by: (UInt8, PossiblePrefix.Element) -> Bool) -> Bool`

Returns a Boolean value indicating whether the initial elements of the sequence are equivalent to the elements in another sequence, using the given predicate as the equivalence test.

`func suffix(Int) -> Slice<DispatchData>`

Returns a subsequence, up to the given maximum length, containing the final elements of the collection.

`func suffix(from: Int) -> Slice<DispatchData>`

Returns a subsequence from the specified position to the end of the collection.