Repeating array in Swift

Question

In Python I can create a repeating list like this:

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

Is there a concise way to do this in

Answer 1

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}

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]

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:)‛

Use instead:

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

or

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

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