Instance Method

max(by:)

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

Declaration

@warn_unqualified_access func max(by areInIncreasingOrder: ((key: Key, value: Value), (key: Key, value: Value)) throws -> Bool) rethrows -> (key: Key, value: Value)?

Parameters

areInIncreasingOrder

A predicate that returns true if its first argument should be ordered before its second argument; otherwise, false.

Return Value

The sequence’s maximum element if the sequence is not empty; otherwise, nil.

Discussion

The predicate must be a strict weak ordering over the elements. That is, for any elements a, b, and c, the following conditions must hold:

  • areInIncreasingOrder(a, a) is always false. (Irreflexivity)

  • If areInIncreasingOrder(a, b) and areInIncreasingOrder(b, c) are both true, then areInIncreasingOrder(a, c) is also true. (Transitive comparability)

  • Two elements are incomparable if neither is ordered before the other according to the predicate. If a and b are incomparable, and b and c are incomparable, then a and c are also incomparable. (Transitive incomparability)

This example shows how to use the max(by:) method on a dictionary to find the key-value pair with the highest value.

let hues = ["Heliotrope": 296, "Coral": 16, "Aquamarine": 156]
let greatestHue = hues.max { a, b in a.value < b.value }
print(greatestHue)
// Prints "Optional(("Heliotrope", 296))"

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 first(where: ((key: Key, value: Value)) -> Bool) -> (key: Key, value: Value)?

Returns the first element of the sequence that satisfies the 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.