Instance Method


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


@warn_unqualified_access func max(by areInIncreasingOrder: (Base.Element, Base.Element) throws -> Bool) rethrows -> Base.Element?



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.


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 }
// Prints "Optional(("Heliotrope", 296))"

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