在Swift中重复数组 [英] Repeating array in Swift

问题描述

在Python中，我可以创建一个重复列表，如下所示:

In Python I can create a repeating list like this:

>>> [1,2,3]*3
[1, 2, 3, 1, 2, 3, 1, 2, 3]

在Swift中有一种简洁的方法吗?

Is there a concise way to do this in Swift?

我能做的最好的事情是:

The best I can do is:

  1> var r = [Int]()
r: [Int] = 0 values
  2> for i in 1...3 { 
  3.     r += [1,2,3]
  4. }
  5> print(r)
[1, 2, 3, 1, 2, 3, 1, 2, 3]

推荐答案

您可以创建2D数组，然后使用flatMap将其转换为1D数组:

You can create a 2D array and then use flatMap to turn it into a 1D array:

let array = [Int](repeating: [1,2,3], count: 3).flatMap{$0}

这是一个扩展，它添加了一个init方法和一个重复方法，该方法采用了一个数组，这使它更简洁:

Here's an extension that adds an init method and a repeating method that takes an array which makes this a bit cleaner:

extension Array {
  init(repeating: [Element], count: Int) {
    self.init([[Element]](repeating: repeating, count: count).flatMap{$0})
  }

  func repeated(count: Int) -> [Element] {
    return [Element](repeating: self, count: count)
  }
}

let array = [1,2,3].repeated(count: 3) // => [1, 2, 3, 1, 2, 3, 1, 2, 3]

请注意，使用新的初始化程序，如果不使用预期的类型就可以得到一个模棱两可的方法调用:

Note that with the new initializer you can get an ambiguous method call if you use it without providing the expected type:

let array = Array(repeating: [1,2,3], count: 3) // Error: Ambiguous use of ‛init(repeating:count:)‛

改为使用:

let array = [Int](repeating: [1,2,3], count: 3) // => [1, 2, 3, 1, 2, 3, 1, 2, 3]

或

let array:[Int] = Array(repeating: [1,2,3], count: 3) // => [1, 2, 3, 1, 2, 3, 1, 2, 3]

如果将方法签名更改为init(repeatingContentsOf: [Element], count: Int)或类似名称，则可以避免这种歧义.

This ambiguity can be avoided if you change the method signature to init(repeatingContentsOf: [Element], count: Int) or similar.

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