Converting shuffle array method from Objective C to Swift (iOS)

Question

I have a method to shuffle an array randomly in Objective-C which works fine, but am having some trouble converting it. Here is the method in Objective-C...

- (NSArray *)shuffle:(NSArray *)array {

NSMutableArray *newArray = [NSMutableArray arrayWithArray:array];

NSUInteger count = [newArray count];

for (NSUInteger i = 0; i < count; i++) {

    NSInteger remainingCount = count - i;

    NSInteger exchangeIndex = i + arc4random_uniform((u_int32_t)remainingCount);

    [newArray exchangeObjectAtIndex:i withObjectAtIndex:exchangeIndex];

}

return [NSArray arrayWithArray:newArray];
}

Here is the Swift version of the method, right below my "figure out error" comment it throws an error saying "Ambiguous use of operator '+'". I'm just trying to cast "remaining count" as a UInt32 for the arc_4random method so I'm not sure what's up. Any ideas? Thank you!

func shuffle(array: NSArray) -> NSArray {

    let newArray : NSMutableArray = NSMutableArray(array: array)

    let count : NSInteger = newArray.count

    for var i = 0; i < count; ++i {

        var remainingCount = count - i

        //figre out error below

        var exchangeIndex = i + arc4random_uniform(UInt32(remainingCount))

        newArray.exchangeObjectAtIndex(i, withObjectAtIndex: exchangeIndex)
    }

    return NSArray(array: newArray)

}

It may caused because the value from "arc4random_uniform(UInt32(remainingCount))" has different type with 'i', i.e. one is UInt32 type, the other is Int type. You may try to cast it to Int: Int(arc4random_uniform(UInt32(remainingCount))) — Surely
– Surely, Commented Feb 20, 2016 at 18:26

Harshal Bhavsar · Accepted Answer · 2016-02-20 18:28:20Z

1

Try This

Updated Working Code

func shuffle(array: NSArray) -> NSArray {

        let newArray : NSMutableArray = NSMutableArray(array: array)

        let count : NSInteger = newArray.count

        for var i = 0; i < count; ++i {

            let remainingCount = count - i

            //figre out error below

            let exchangeIndex = i + Int(arc4random_uniform(UInt32(remainingCount)))

            newArray.exchangeObjectAtIndex(i, withObjectAtIndex: exchangeIndex)
        }

        return NSArray(array: newArray)

    }

Casted the result of arc4random_uniform to Int

answered Feb 20, 2016 at 18:28

Harshal Bhavsar

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Community · Accepted Answer · 2020-06-20 09:12:55Z

1

Swift 4.2

Now, from Swift 4.2 the feature is built into Swift. You can shuffle an array either in-place or create a new shuffled array.

var albums = ["Red", "1989", "Reputation"]

// shuffle in place
albums.shuffle()

// get a shuffled array back
let shuffled = albums.shuffled()

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Dec 23, 2018 at 18:19

Md. Ibrahim Hassan

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Comments

user3441734 · Accepted Answer · 2016-02-20 19:12:26Z

0

how to shuffle an array

import Foundation // arc4random_uniforn

extension Array {
    func shuffle()->Array {
        var arr = self
        let c = UInt32(arr.count)
        for i in 0..<(c-1) {
            let j = arc4random_uniform(c)
            if i != j {
                swap(&arr[Int(i)], &arr[Int(j)])
            }        
        }
        return arr
    }
}

let arr0 = [1,2,3,4,5,6,7,8,9,0]
for i in 0..<5 {
    print(arr0.shuffle())
}
/*
[6, 4, 0, 1, 8, 9, 3, 5, 2, 7]
[5, 2, 3, 9, 8, 1, 7, 6, 4, 0]
[8, 7, 6, 1, 2, 4, 9, 5, 0, 3]
[2, 4, 7, 6, 5, 9, 8, 1, 0, 3]
[7, 5, 6, 1, 9, 4, 2, 8, 3, 0]
*/

randomly and uniformly ... Why your code doesn't compile, is explained in note made by @z_px

edited Feb 20, 2016 at 19:12

answered Feb 20, 2016 at 18:49

user3441734

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