How do I shuffle an array in Swift?

Question

How do I randomize or shuffle the elements within an array in Swift? For example, if my array consists of 52 playing cards, I want to shuffle the array in o

Answer 1

This is a version of Nate's implementation of the Fisher-Yates shuffle for Swift 4 (Xcode 9).

extension MutableCollection {
    /// Shuffle the elements of `self` in-place.
    mutating func shuffle() {
        for i in indices.dropLast() {
            let diff = distance(from: i, to: endIndex)
            let j = index(i, offsetBy: numericCast(arc4random_uniform(numericCast(diff))))
            swapAt(i, j)
        }
    }
}

extension Collection {
    /// Return a copy of `self` with its elements shuffled
    func shuffled() -> [Element] {
        var list = Array(self)
        list.shuffle()
        return list
    }
}

The changes are:

• The constraint Indices.Iterator.Element == Index is now part of the Collection protocol, and need not be imposed on the extension anymore.
• Exchanging elements must done by calling swapAt() on the collection, compare SE-0173 Add MutableCollection.swapAt(_:_:).
• Element is an alias for Iterator.Element.