我有一个像这样的数组:
var names: String = [ "Peter", "Steve", "Max", "Sandra", "Roman", "Julia" ]
我想从该数组中获取3个随机元素。我来自C#,但是我不确定该从哪里开始。我想我应该先对数组进行随机排序,然后再从中选择前3个项目?
我尝试使用以下扩展名将其改组:
extension Array { mutating func shuffle() { for _ in 0..<10 { sort { (_,_) in arc4random() < arc4random() } } } }
但随后在“ shuffle()”的位置说“’()’不可转换为’[Int]’”。
为了挑选一些元素,我使用:
var randomPicks = names[0..<4];
到目前为止看起来还不错。
如何洗牌?还是有人对此有更好/更优雅的解决方案?
Xcode 11•Swift 5.1
extension Collection { func choose(_ n: Int) -> ArraySlice<Element> { shuffled().prefix(n) } }
游乐场测试
var alphabet = ["A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"] let shuffledAlphabet = alphabet.shuffled() // "O", "X", "L", "D", "N", "K", "R", "E", "S", "Z", "I", "T", "H", "C", "U", "B", "W", "M", "Q", "Y", "V", "A", "G", "P", "F", "J"] let letter = alphabet.randomElement() // "D" var numbers = Array(0...9) let shuffledNumbers = numbers.shuffled() shuffledNumbers // [8, 9, 3, 6, 0, 1, 4, 2, 5, 7] numbers // [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] numbers.shuffle() // mutate it [6, 0, 2, 3, 9, 1, 5, 7, 4, 8] numbers // [6, 0, 2, 3, 9, 1, 5, 7, 4, 8] let pick3numbers = numbers.choose(3) // [8, 9, 2]
extension RangeReplaceableCollection { /// Returns a new Collection shuffled var shuffled: Self { .init(shuffled()) } /// Shuffles this Collection in place @discardableResult mutating func shuffledInPlace() -> Self { self = shuffled return self } func choose(_ n: Int) -> SubSequence { shuffled.prefix(n) } }
var alphabetString = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" let shuffledAlphabetString = alphabetString.shuffled // "DRGXNSJLFQHPUZTBKVMYAWEICO" let character = alphabetString.randomElement() // "K" alphabetString.shuffledInPlace() // mutate it "WYQVBLGZKPFUJTHOXERADMCINS" alphabetString // "WYQVBLGZKPFUJTHOXERADMCINS" let pick3Characters = alphabetString.choose(3) // "VYA"