How do I shuffle an array in Swift?

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 order to shuffle the deck.

array.shuffle

25 Answers
25

This answer details how to shuffle with a fast and uniform algorithm (Fisher-Yates) in Swift 4.2+ and how to add the same feature in the various previous versions of Swift. The naming and behavior for each Swift version matches the mutating and nonmutating sorting methods for that version.

Swift 4.2+

shuffle and shuffled are native starting Swift 4.2. Example usage:

shuffle

shuffled

let x = [1, 2, 3].shuffled()
// x == [2, 3, 1]

let fiveStrings = stride(from: 0, through: 100, by: 5).map(String.init).shuffled()
// fiveStrings == ["20", "45", "70", "30", ...]

var numbers = [1, 2, 3, 4]
numbers.shuffle()
// numbers == [3, 2, 1, 4]


Swift 4.0 and 4.1

These extensions add a shuffle() method to any mutable collection (arrays and unsafe mutable buffers) and a shuffled() method to any sequence:

shuffle()

shuffled()

extension MutableCollection
/// Shuffles the contents of this collection.
mutating func shuffle()
let c = count
guard c > 1 else return

for (firstUnshuffled, unshuffledCount) in zip(indices, stride(from: c, to: 1, by: -1))
// Change `Int` in the next line to `IndexDistance` in < Swift 4.1
let d: Int = numericCast(arc4random_uniform(numericCast(unshuffledCount)))
let i = index(firstUnshuffled, offsetBy: d)
swapAt(firstUnshuffled, i)




extension Sequence
/// Returns an array with the contents of this sequence, shuffled.
func shuffled() -> [Element]
var result = Array(self)
result.shuffle()
return result




Same usage as in Swift 4.2 examples above.

Swift 3

These extensions add a shuffle() method to any mutable collection and a shuffled() method to any sequence:

shuffle()

shuffled()

extension MutableCollection where Indices.Iterator.Element == Index
/// Shuffles the contents of this collection.
mutating func shuffle()
let c = count
guard c > 1 else return

for (firstUnshuffled , unshuffledCount) in zip(indices, stride(from: c, to: 1, by: -1))
// Change `Int` in the next line to `IndexDistance` in < Swift 3.2
let d: Int = numericCast(arc4random_uniform(numericCast(unshuffledCount)))
guard d != 0 else continue
let i = index(firstUnshuffled, offsetBy: d)
self.swapAt(firstUnshuffled, i)




extension Sequence
/// Returns an array with the contents of this sequence, shuffled.
func shuffled() -> [Iterator.Element]
var result = Array(self)
result.shuffle()
return result




Same usage as in Swift 4.2 examples above.

Swift 2

(obsolete language: you can't use Swift 2.x to publish on iTunes Connect starting July 2018)

extension MutableCollectionType where Index == Int
/// Shuffle the elements of `self` in-place.
mutating func shuffleInPlace()
// empty and single-element collections don't shuffle
if count < 2 return

for i in startIndex ..< endIndex - 1
let j = Int(arc4random_uniform(UInt32(count - i))) + i
guard i != j else continue
swap(&self[i], &self[j])




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




Usage:

[1, 2, 3].shuffle()
// [2, 3, 1]

let fiveStrings = 0.stride(through: 100, by: 5).map(String.init).shuffle()
// ["20", "45", "70", "30", ...]

var numbers = [1, 2, 3, 4]
numbers.shuffleInPlace()
// [3, 2, 1, 4]


Swift 1.2

(obsolete language: you can't use Swift 1.x to publish on iTunes Connect starting July 2018)

shuffle

This extension will let you shuffle a mutable Array instance in place:

Array

extension Array
mutating func shuffle()
if count < 2 return
for i in 0..<(count - 1)
let j = Int(arc4random_uniform(UInt32(count - i))) + i
swap(&self[i], &self[j])



var numbers = [1, 2, 3, 4, 5, 6, 7, 8]
numbers.shuffle() // e.g., numbers == [6, 1, 8, 3, 2, 4, 7, 5]


shuffled

This extension will let you retrieve a shuffled copy of an Array instance:

Array

extension Array
func shuffled() -> [T]
if count < 2 return self
var list = self
for i in 0..<(list.count - 1)
let j = Int(arc4random_uniform(UInt32(list.count - i))) + i
swap(&list[i], &list[j])

return list


let numbers = [1, 2, 3, 4, 5, 6, 7, 8]
let mixedup = numbers.shuffled() // e.g., mixedup == [6, 1, 8, 3, 2, 4, 7, 5]


countElements

count

T.Index.Distance

C.Index.Distance == Int

[1, 2].shuffled()

[2, 1]

guard i != j else continue

shuffleInPlace

for i in 0..<count - 1

for i in startIndex ..< endIndex - 1

Edit: As noted in other answers, Swift 4.2 finally adds random number generation to the standard library, complete with array shuffling.

However, the GKRandom / GKRandomDistribution suite in GameplayKit can still be useful with the new RandomNumberGenerator protocol — if you add extensions to the GameplayKit RNGs to conform to the new standard library protocol, you can easily get:

GKRandom

GKRandomDistribution

RandomNumberGenerator

...and still make use of the nice new "native" random APIs in Swift.

The rest of this answer concerns such RNGs and/or their use in older Swift compilers.

There are some good answers here already, as well as some good illustrations of why writing your own shuffle can be error-prone if you're not careful.

In iOS 9, macOS 10.11, and tvOS 9 (or later), you don't have to write your own. There's an efficient, correct implementation of Fisher-Yates in GameplayKit (which, despite the name, is not just for games).

If you just want a unique shuffle:

let shuffled = GKRandomSource.sharedRandom().arrayByShufflingObjects(in: array)


If you want to be able to replicate a shuffle or series of shuffles, choose and seed a specific random source; e.g.

let lcg = GKLinearCongruentialRandomSource(seed: mySeedValue)
let shuffled = lcg.arrayByShufflingObjects(in: array)


In iOS 10 / macOS 10.12 / tvOS 10, there's also a convenience syntax for shuffling via an extension on NSArray. Of course, that's a little cumbersome when you're using a Swift Array (and it loses its element type on coming back to Swift):

NSArray

Array

let shuffled1 = (array as NSArray).shuffled(using: random) // -> [Any]
let shuffled2 = (array as NSArray).shuffled() // use default random source


But it's pretty easy to make a type-preserving Swift wrapper for it:

extension Array
func shuffled(using source: GKRandomSource) -> [Element]
return (self as NSArray).shuffled(using: source) as! [Element]

func shuffled() -> [Element]
return (self as NSArray).shuffled() as! [Element]


let shuffled3 = array.shuffled(using: random)
let shuffled4 = array.shuffled()


let shuffled = lcg.arrayByShufflingObjects(in: array)

In Swift 2.0, GameplayKit may come to the rescue! (supported by iOS9 or later)

import GameplayKit

func shuffle()
array = GKRandomSource.sharedRandom().arrayByShufflingObjectsInArray(array)



import GameplayKit.GKRandomSource

Here's something possibly a little shorter:

sorted(a) _, _ in arc4random() % 2 == 0


sort

arc4random_uniform()

collection.sorted _,_ in arc4random_uniform(1) == 0

Taking Nate's algorithm I wanted to see how this would look with Swift 2 and protocol extensions.

This is what I came up with.

extension MutableCollectionType where Self.Index == Int
mutating func shuffleInPlace()
let c = self.count
for i in 0..<(c - 1)
let j = Int(arc4random_uniform(UInt32(c - i))) + i
swap(&self[i], &self[j])




extension MutableCollectionType where Self.Index == Int
func shuffle() -> Self
var r = self
let c = self.count
for i in 0..<(c - 1)
let j = Int(arc4random_uniform(UInt32(c - i))) + i
swap(&r[i], &r[j])

return r




Now, any MutableCollectionType can use these methods given it uses Int as an Index

MutableCollectionType

Int

Index

In my case, I had some problems of swapping objects in Array. Then I scratched my head and go for reinventing the wheel.

// swift 3.0 ready
extension Array

func shuffled() -> [Element]
var results = [Element]()
var indexes = (0 ..< count).map $0
while indexes.count > 0
let indexOfIndexes = Int(arc4random_uniform(UInt32(indexes.count)))
let index = indexes[indexOfIndexes]
results.append(self[index])
indexes.remove(at: indexOfIndexes)

return results





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:

Indices.Iterator.Element == Index

Collection

swapAt()

MutableCollection.swapAt(_:_:)

Element

Iterator.Element

This is what I use:

func newShuffledArray(array:NSArray) -> NSArray
var mutableArray = array.mutableCopy() as! NSMutableArray
var count = mutableArray.count
if count>1
for var i=count-1;i>0;--i
mutableArray.exchangeObjectAtIndex(i, withObjectAtIndex: Int(arc4random_uniform(UInt32(i+1))))


return mutableArray as NSArray



Swift 4
Shuffle the elements of an array in a for loop where i is the mixing ratio

var cards = [Int]() //Some Array
let i = 4 // is the mixing ratio
func shuffleCards()
for _ in 0 ..< cards.count * i
let card = cards.remove(at: Int(arc4random_uniform(UInt32(cards.count))))
cards.insert(card, at: Int(arc4random_uniform(UInt32(cards.count))))




Or with extension Int

func shuffleCards()
for _ in 0 ..< cards.count * i
let card = cards.remove(at: cards.count.arc4random)
cards.insert(card, at: cards.count.arc4random)


extension Int
var arc4random: Int
if self > 0
print("Arc for random positiv self (Int(arc4random_uniform(UInt32(self))))")
return Int(arc4random_uniform(UInt32(self)))
else if self < 0
print("Arc for random negotiv self (-Int(arc4random_uniform(UInt32(abs(self)))))")
return -Int(arc4random_uniform(UInt32(abs(self))))
else
print("Arc for random equal 0")
return 0





Swift 3 solution, following @Nate Cook answer: (work if the index starts with 0, see comments below)

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


extension MutableCollection where Index == Int
/// Shuffle the elements of `self` in-place.
mutating func shuffleInPlace()
// empty and single-element collections don't shuffle
if count < 2 return
let countInt = count as! Int

for i in 0..<countInt - 1
let j = Int(arc4random_uniform(UInt32(countInt - i))) + i
guard i != j else continue
swap(&self[i], &self[j])





var a = [1, 2, 3, 4, 5, 6][3..<6]; a.shuffleInPlace()

This is how its done in a Simplest way.import Gamplaykit to your VC and use the below code. Tested in Xcode 8.

import Gamplaykit

import GameplayKit

let array: NSArray = ["Jock", "Ellie", "Sue Ellen", "Bobby", "JR", "Pamela"]

override func viewDidLoad()
super.viewDidLoad()

print(array.shuffled())



If you want to get a shuffled String from an Array you can use below code..

func suffleString()

let ShuffleArray = array.shuffled()

suffleString.text = ShuffleArray.first as? String

print(suffleString.text!)




With Swift 3, if you want to shuffle an array in place or get a new shuffled array from an array, AnyIterator can help you. The idea is to create an array of indices from your array, to shuffle those indices with an AnyIterator instance and swap(_:_:) function and to map each element of this AnyIterator instance with the array's corresponding element.

AnyIterator

AnyIterator

swap(_:_:)

AnyIterator

The following Playground code shows how it works:

import Darwin // required for arc4random_uniform

let array = ["Jock", "Ellie", "Sue Ellen", "Bobby", "JR", "Pamela"]
var indexArray = Array(array.indices)
var index = indexArray.endIndex

let indexIterator: AnyIterator<Int> = AnyIterator
guard let nextIndex = indexArray.index(index, offsetBy: -1, limitedBy: indexArray.startIndex)
else return nil

index = nextIndex
let randomIndex = Int(arc4random_uniform(UInt32(index)))
if randomIndex != index
swap(&indexArray[randomIndex], &indexArray[index])


return indexArray[index]


let newArray = indexIterator.map array[$0]
print(newArray) // may print: ["Jock", "Ellie", "Sue Ellen", "JR", "Pamela", "Bobby"]


You can refactor the previous code and create a shuffled() function inside an Array extension in order to get a new shuffled array from an array:

shuffled()

Array

import Darwin // required for arc4random_uniform

extension Array

func shuffled() -> Array<Element>
var indexArray = Array<Int>(indices)
var index = indexArray.endIndex

let indexIterator = AnyIterator<Int>
guard let nextIndex = indexArray.index(index, offsetBy: -1, limitedBy: indexArray.startIndex)
else return nil

index = nextIndex
let randomIndex = Int(arc4random_uniform(UInt32(index)))
if randomIndex != index
swap(&indexArray[randomIndex], &indexArray[index])


return indexArray[index]


return indexIterator.map self[$0]





Usage:

let array = ["Jock", "Ellie", "Sue Ellen", "Bobby", "JR", "Pamela"]
let newArray = array.shuffled()
print(newArray) // may print: ["Bobby", "Pamela", "Jock", "Ellie", "JR", "Sue Ellen"]


let emptyArray = [String]()
let newEmptyArray = emptyArray.shuffled()
print(newEmptyArray) // prints:


As an alternative to the previous code, you can create a shuffle() function inside an Array extension in order to shuffle an array in place:

shuffle()

Array

import Darwin // required for arc4random_uniform

extension Array

mutating func shuffle()
var indexArray = Array<Int>(indices)
var index = indexArray.endIndex

let indexIterator = AnyIterator<Int>
guard let nextIndex = indexArray.index(index, offsetBy: -1, limitedBy: indexArray.startIndex)
else return nil

index = nextIndex
let randomIndex = Int(arc4random_uniform(UInt32(index)))
if randomIndex != index
swap(&indexArray[randomIndex], &indexArray[index])


return indexArray[index]


self = indexIterator.map self[$0]





Usage:

var mutatingArray = ["Jock", "Ellie", "Sue Ellen", "Bobby", "JR", "Pamela"]
mutatingArray.shuffle()
print(mutatingArray) // may print ["Sue Ellen", "Pamela", "Jock", "Ellie", "Bobby", "JR"]


Form the article of Fisher–Yates shuffle on Wikipedia

Swift 3.1,4.0

a). Pencil-and-paper method :

func shuffle<T>(_ array:inout [T])

var temp = [T]()

for _ in array

/*Generating random number with length*/
let random = arc4random_uniform(UInt32(array.count))
/*Take the element from array*/
let elementTaken = array[Int(random)]
/*Append it to new tempArray*/
temp.append(elementTaken)
/*Remove the element from array*/
array.remove(at: Int(random))


/* array = tempArray*/
array = temp



b). Modern method:(Durstenfeld's version)

func shuffle<T>(_ array:inout [T])

var length = array.count

for _ in array

/*Generating random number with length*/
let random = arc4random_uniform(UInt32(length))
/*Check before index of two elements not same*/
if length-1 != Int(random)
swap(&array[length-1], &array[Int(random)])


length -= 1




Extension:

Extension:

a). Pencil-and-paper method :

extension Array

mutating func shuffled()

var temp = [Element]()

for _ in self

/*Generating random number with length*/
let random = arc4random_uniform(UInt32(self.count))
/*Take the element from array*/
let elementTaken = self[Int(random)]
/*Append it to new tempArray*/
temp.append(elementTaken)
/*Remove the element from array*/
self.remove(at: Int(random))


/* array = tempArray*/
self = temp




b). Modern method:(Durstenfeld's version)

extension Array

mutating func shuffled()

var length = self.count

for _ in self

/*Generating random number with length*/
let random = arc4random_uniform(UInt32(length))

/*Check before index of two elements not same*/

if length-1 != Int(random)

/*Swaping elements, If same index then there is no swap*/
// swap(&self[length-1], &self[Int(random)]) -> Swift 3.0
self.swapAt(length-1, Int(random)) //-> Swift 4.0



length -= 1





Reference :

/* By using shuffle functions*/
var a = [1,2,3,4,5,6,7,8,9,10]

for _ in 1...10

self.shuffle(&a)

/*For shuffled extension, a.shuffled()*/
print(a)



Note:
You can use empty array also.

Output:

[6, 2, 10, 5, 1, 8, 9, 4, 3, 7]

[7, 1, 9, 8, 2, 10, 5, 6, 4, 3]

[8, 9, 6, 10, 5, 2, 7, 4, 3, 1]

[10, 1, 7, 4, 8, 9, 3, 5, 2, 6]

[8, 1, 6, 9, 3, 7, 4, 5, 10, 2]

[4, 3, 7, 9, 1, 5, 8, 6, 10, 2]

[7, 3, 4, 9, 10, 1, 6, 5, 2, 8]

[3, 6, 2, 4, 5, 8, 9, 7, 1, 10]

[5, 1, 2, 10, 6, 9, 7, 3, 8, 4]

[7, 9, 3, 8, 2, 1, 5, 4, 6, 10]

Please let me know if any queries, Other Swift version will be check soon.

You can use generic swap function as well and implement mentioned Fisher-Yates:

swap

for idx in 0..<arr.count
let rnd = Int(arc4random_uniform(UInt32(idx)))
if rnd != idx
swap(&arr[idx], &arr[rnd])




or less verbose:

for idx in 0..<steps.count
swap(&steps[idx], &steps[Int(arc4random_uniform(UInt32(idx)))])



let rnd = Int(arc4random_uniform(UInt32(idx + 1)))

arr.count - 1

1

0

arr.count - 1

works!!. organisms is the array to shuffle.

extension Array

/** Randomizes the order of an array's elements. */
mutating func shuffle()

for _ in 0..<10

sort (_,_) in arc4random() < arc4random()




var organisms = [
"ant", "bacteria", "cougar",
"dog", "elephant", "firefly",
"goat", "hedgehog", "iguana"]

print("Original: (organisms)")

organisms.shuffle()

print("Shuffled: (organisms)")


This is how to shuffle one array with a seed in Swift 3.0.

extension MutableCollection where Indices.Iterator.Element == Index
mutating func shuffle()
let c = count
guard c > 1 else return


for (firstUnshuffled , unshuffledCount) in zip(indices, stride(from: c, to: 1, by: -1))
srand48(seedNumber)
let number:Int = numericCast(unshuffledCount)
let r = floor(drand48() * Double(number))

let d: IndexDistance = numericCast(Int(r))
guard d != 0 else continue
let i = index(firstUnshuffled, offsetBy: d)
swap(&self[firstUnshuffled], &self[i])





let shuffl = GKRandomSource.sharedRandom().arrayByShufflingObjects(in: arrayObject)


This is what I use:

import GameplayKit

extension Collection
func shuffled() -> [Iterator.Element]
let shuffledArray = (self as? NSArray)?.shuffled()
let outputArray = shuffledArray as? [Iterator.Element]
return outputArray ??

mutating func shuffle()
if let selfShuffled = self.shuffled() as? Self
self = selfShuffled




// Usage example:

var numbers = [1,2,3,4,5]
numbers.shuffle()

print(numbers) // output example: [2, 3, 5, 4, 1]

print([10, "hi", 9.0].shuffled()) // output example: [hi, 10, 9]


Simple Example:

extension Array
mutating func shuffled()
for _ in self
// generate random indexes that will be swapped
var (a, b) = (Int(arc4random_uniform(UInt32(self.count - 1))), Int(arc4random_uniform(UInt32(self.count - 1))))
if a == b // if the same indexes are generated swap the first and last
a = 0
b = self.count - 1

swap(&self[a], &self[b])




var array = [1,2,3,4,5,6,7,8,9,10]
array.shuffled()
print(array) // [9, 8, 3, 5, 7, 6, 4, 2, 1, 10]


Working Array Extension (mutating & non-mutating)

The top answer is deprecated, so I took it upon myself to create my own extension to shuffle an array in the newest version of Swift, Swift 4.1 (Xcode 9):

extension Array

// Non-mutating shuffle
var shuffled : Array
let totalCount : Int = self.count
var shuffledArray : Array =
var count : Int = totalCount
var tempArray : Array = self
for _ in 0..<totalCount
let randomIndex : Int = Int(arc4random_uniform(UInt32(count)))
let randomElement : Element = tempArray.remove(at: randomIndex)
shuffledArray.append(randomElement)
count -= 1

return shuffledArray


// Mutating shuffle
mutating func shuffle()
let totalCount : Int = self.count
var shuffledArray : Array =
var count : Int = totalCount
var tempArray : Array = self
for _ in 0..<totalCount
let randomIndex : Int = Int(arc4random_uniform(UInt32(count)))
let randomElement : Element = tempArray.remove(at: randomIndex)
shuffledArray.append(randomElement)
count -= 1

self = shuffledArray




[Array] -> [Array]

let array = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]

print(array.shuffled)


This prints array in a random order.

array

[Array] = [Array]

var array = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]

array.shuffle()
// The array has now been mutated and contains all of its initial
// values, but in a randomized shuffled order

print(array)


This prints array in its current order, which has already been randomly shuffled.

array

Hopes this works for everybody, if you have any questions, suggestions, or comments, feel free to ask!

In SWIFT 4

func createShuffledSequenceOfNumbers(max:UInt)->[UInt]

var array:[UInt]! =
var myArray:[UInt]! =
for i in 1...max
myArray.append(i)

for i in 1...max
array.append(i)

var tempArray:[Int]! =
for index in 0...(myArray.count - 1)

var isNotFinded:Bool = true
while(isNotFinded)

let randomNumber = arc4random_uniform(UInt32(myArray.count))
let randomIndex = Int(randomNumber)

if(!tempArray.contains(randomIndex))
tempArray.append(randomIndex)

array[randomIndex] = myArray[index]
isNotFinded = false




return array



In Swift 4.2, there is now a method for both a mutable shuffle and immutable shuffled. You can read more about the random generation and array stuff here.

shuffle

shuffled

If you want to use simple Swift For loop function use this ->

var arrayItems = ["A1", "B2", "C3", "D4", "E5", "F6", "G7", "H8", "X9", "Y10", "Z11"]
var shuffledArray = [String]()

for i in 0..<arrayItems.count

let randomObject = Int(arc4random_uniform(UInt32(items.count)))

shuffledArray.append(items[randomObject])

items.remove(at: randomObject)


print(shuffledArray)


Swift Array suffle using extension ->

extension Array
// Order Randomize
mutating func shuffle()
for _ in 0..<count
sort (_,_) in arc4random() < arc4random()





Here's some code that runs in playground. You won't need to import Darwin in an actual Xcode project.

import darwin

var a = [1,2,3,4,5,6,7]

func shuffle<ItemType>(item1: ItemType, item2: ItemType) -> Bool
return drand48() > 0.5


sort(a, shuffle)

println(a)


drand48()

srand48(Int(arc4random()))

It stop at "swap(&self[i], &self[j])" when I upgrade the xCode version to 7.4 beta.

fatal error: swapping a location with itself is not supported

I found the reason that i = j (function of swap will exploded)

So I add a condition as below

if (i != j)
swap(&list[i], &list[j])



YA! It's OK for me.

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