What's the Best Way to Shuffle an NSMutableArray?

From iOS 10, you can use [NSArray `shuffled()` from GameplayKit](

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). Here is an helper for Array in Swift 3:

import GameplayKit

extension Array {
@available(iOS 10.0, macOS 10.12, tvOS 10.0, *)
func shuffled() -> [Element] {
return (self as NSArray).shuffled() as! [Element]
}
@available(iOS 10.0, macOS 10.12, tvOS 10.0, *)
mutating func shuffle() {
replaceSubrange(0..<count, with: shuffled())
}
}

A slightly improved and concise solution (compared to the top answers).

The algorithm is the same and is described in literature as "[Fisher-Yates shuffle](

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;.

In Objective-C:

@implementation NSMutableArray (Shuffle)
// Fisher-Yates shuffle
- (void)shuffle
{
for (NSUInteger i = self.count; i > 1; i--)
[self exchangeObjectAtIndex:i - 1 withObjectAtIndex:arc4random_uniform((u_int32_t)i)];
}
@end

In Swift 3.2 and 4.x:

extension Array {
/// Fisher-Yates shuffle
mutating func shuffle() {
for i in stride(from: count - 1, to: 0, by: -1) {
swapAt(i, Int(arc4random_uniform(UInt32(i + 1))))
}
}
}

In Swift 3.0 and 3.1:

extension Array {
/// Fisher-Yates shuffle
mutating func shuffle() {
for i in stride(from: count - 1, to: 0, by: -1) {
let j = Int(arc4random_uniform(UInt32(i + 1)))
(self[i], self[j]) = (self[j], self[i])
}
}
}

Note: [A more concise solution in Swift is possible from iOS10 using `GameplayKit`.](

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)

Note: [An algorithm for unstable shuffling (with all positions forced to change if count > 1) is also available](

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)

If you import `GameplayKit`, there is a `shuffled` API:

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let shuffledArray = array.shuffled()