Instance Method

first(where:)

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

Declaration

func first(where predicate: ((key: Key, value: Value)) throws -> Bool) rethrows -> (key: Key, value: Value)?

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:

let numbers = [3, 7, 4, -2, 9, -6, 10, 1]
if let firstNegative = numbers.first(where: { $0 < 0 }) {
    print("The first negative number is \(firstNegative).")
}
// Prints "The first negative number is -2."

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

See Also

Finding Elements

func contains(where: ((key: Key, value: Value)) -> Bool) -> Bool

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

func allSatisfy(((key: Key, value: Value)) -> Bool) -> Bool

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

func firstIndex(where: ((key: Key, value: Value)) -> Bool) -> Index?

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

func min(by: ((key: Key, value: Value), (key: Key, value: Value)) -> Bool) -> (key: Key, value: Value)?

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

func max(by: ((key: Key, value: Value), (key: Key, value: Value)) -> Bool) -> (key: Key, value: Value)?

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