Contents

min(by:)

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

Declaration

@warn_unqualified_access func min(by areInIncreasingOrder: (Self.Element, Self.Element) async throws -> Bool) async rethrows -> Self.Element?

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 minimum element, according to areInIncreasingOrder. If the sequence has no elements, returns nil.

Discussion

Use this method when the asynchronous sequence’s values don’t conform to Comparable, or when you want to apply a custom ordering to the sequence.

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)

The following example uses an enumeration of playing cards ranks, Rank, which ranges from ace (low) to king (high). An asynchronous sequence called RankCounter produces all elements of the array. The predicate provided to the min(by:) method sorts ranks based on their rawValue:

enum Rank: Int {
    case ace = 1, two, three, four, five, six, seven, eight, nine, ten, jack, queen, king
}

let min = await RankCounter()
    .min { $0.rawValue < $1.rawValue }
print(min ?? "none")
// Prints "ace"

See Also

Accessing an Asynchronous Sequence of Results