如何在Swift中对数组进行混洗？

如何在Swift中对数组进行混洗？

该答案详细说明了如何在Swift 4.2+中使用快速统一的算法（Fisher-
Yates）进行改组，以及如何在各个早期版本的Swift中添加相同功能。每个Swift版本的命名和行为都与该版本的变异和非变异排序方法匹配。

迅捷4.2+

shuffle

并且

shuffled

是从Swift
4.2开始原生的 用法示例：

let x = [1, 2, 3].shuffled()// x == [2, 3, 1]let fiveStrings = stride(from: 0, through: 100, by: 5).map(String.init).shuffled()// fiveStrings == ["20", "45", "70", "30", ...]var numbers = [1, 2, 3, 4]numbers.shuffle()// numbers == [3, 2, 1, 4]

Swift 4.0和4.1

这些扩展将

shuffle()

方法添加到任何可变集合（数组和不安全的可变缓冲区），并

shuffled()

在任何序列上添加方法：

extension MutableCollection {    /// Shuffles the contents of this collection.    mutating func shuffle() {        let c = count        guard c > 1 else { return }        for (firstUnshuffled, unshuffledCount) in zip(indices, stride(from: c, to: 1, by: -1)) { // Change `Int` in the next line to `IndexDistance` in < Swift 4.1 let d: Int = numericCast(arc4random_uniform(numericCast(unshuffledCount))) let i = index(firstUnshuffled, offsetBy: d) swapAt(firstUnshuffled, i)        }    }}extension Sequence {    /// Returns an array with the contents of this sequence, shuffled.    func shuffled() -> [Element] {        var result = Array(self)        result.shuffle()        return result    }}

与上述Swift 4.2示例中的用法相同。

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迅捷3

这些扩展将

shuffle()

方法添加到任何可变集合中，并将

shuffled()

方法添加到任何序列中：

extension MutableCollection where Indices.Iterator.Element == Index {    /// Shuffles the contents of this collection.    mutating func shuffle() {        let c = count        guard c > 1 else { return }        for (firstUnshuffled , unshuffledCount) in zip(indices, stride(from: c, to: 1, by: -1)) { // Change `Int` in the next line to `IndexDistance` in < Swift 3.2 let d: Int = numericCast(arc4random_uniform(numericCast(unshuffledCount))) guard d != 0 else { continue } let i = index(firstUnshuffled, offsetBy: d) self.swapAt(firstUnshuffled, i)        }    }}extension Sequence {    /// Returns an array with the contents of this sequence, shuffled.    func shuffled() -> [Iterator.Element] {        var result = Array(self)        result.shuffle()        return result    }}

与上述Swift 4.2示例中的用法相同。

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迅捷2

（过时的语言：自2018年7月起，您将无法使用Swift 2.x在iTunes Connect上发布）

extension MutableCollectionType where Index == Int {    /// Shuffle the elements of `self` in-place.    mutating func shuffleInPlace() {        // empty and single-element collections don't shuffle        if count < 2 { return }        for i in startIndex ..< endIndex - 1 { let j = Int(arc4random_uniform(UInt32(count - i))) + i guard i != j else { continue } swap(&self[i], &self[j])        }    }}extension CollectionType {    /// Return a copy of `self` with its elements shuffled.    func shuffle() -> [Generator.Element] {        var list = Array(self)        list.shuffleInPlace()        return list    }}

用法：

[1, 2, 3].shuffle()// [2, 3, 1]let fiveStrings = 0.stride(through: 100, by: 5).map(String.init).shuffle()// ["20", "45", "70", "30", ...]var numbers = [1, 2, 3, 4]numbers.shuffleInPlace()// [3, 2, 1, 4]

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斯威夫特1.2

（过时的语言：自2018年7月起，您将无法使用Swift 1.x在iTunes Connect上发布）

shuffle

作为变异数组方法

通过此扩展，您可以

Array

在适当位置随机播放可变实例：

extension Array {    mutating func shuffle() {        if count < 2 { return }        for i in 0..<(count - 1) { let j = Int(arc4random_uniform(UInt32(count - i))) + i swap(&self[i], &self[j])        }    }}var numbers = [1, 2, 3, 4, 5, 6, 7, 8]numbers.shuffle()          // e.g., numbers == [6, 1, 8, 3, 2, 4, 7, 5]

shuffled

作为非变异数组方法

通过此扩展，您可以检索

Array

实例的随机组合副本：

extension Array {    func shuffled() -> [T] {        if count < 2 { return self }        var list = self        for i in 0..<(list.count - 1) { let j = Int(arc4random_uniform(UInt32(list.count - i))) + i swap(&list[i], &list[j])        }        return list    }}let numbers = [1, 2, 3, 4, 5, 6, 7, 8]let mixedup = numbers.shuffled()     // e.g., mixedup == [6, 1, 8, 3, 2, 4, 7, 5]