Re-arrange NSArray/MSMutableArray in random order

Question

I'm using NSArray/NSMutable array to store different objects. Once all the objects are added, I want to re-arrange them in random order. How can I do it?

score 55 · Accepted Answer · answered Nov 17 '10 at 07:19

NSUInteger count = [yourMutableArray count];
for (NSUInteger i = 0; i < count; ++i) {
// Select a random element between i and end of array to swap with.
   int nElements = count - i;
   int n = (arc4random() % nElements) + i;
   [yourMutableArray exchangeObjectAtIndex:i withObjectAtIndex:n];
}

score 27 · Answer 2 · answered Oct 21 '12 at 13:34

27

// the Knuth shuffle
for (NSInteger i = array.count-1; i > 0; i--)
{
    [array exchangeObjectAtIndex:i withObjectAtIndex:arc4random_uniform(i+1)];
}

answered Oct 21 '12 at 13:34

jwwatts

271
3
2

Best solution if you target your app iOS >= 4.3. `__OSX_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_4_3)` – Hemang Oct 22 '12 at 05:56
why do you iterate from n -> 0 and not 0 -> n – Peter Lapisu Dec 05 '14 at 23:38
@Peter He iterates backwards because he doesn't want to get the count at every iteration and the direction doesn't matter since we're randomizing it anyway. Keeps the line count down. – Robert Nall Jan 15 '15 at 02:16

score 1 · Answer 3 · answered May 01 '18 at 16:01

1

Link GameplayKit/GameplayKit.h in your project then

#import <GameplayKit/GameplayKit.h>

Now you can use the property shuffledArray.

NSArray *randomArray = [yourArray shuffledArray];

answered May 01 '18 at 16:01

John Franke

1,444
19
23

score 0 · Answer 4 · answered Feb 07 '19 at 13:31

0

Swift 4

let count = self.arrayOfData.count
for (index, _) in self.arrayOfData.enumerated()
{
  let nTempElement = count - index
  let swapIndexwith = (Int(arc4random()) % nTempElement) + index
  arrayOfData.swapAt(index, swapIndexwith)
}

answered Feb 07 '19 at 13:31

nimesh surani

177
1
13

Re-arrange NSArray/MSMutableArray in random order

4 Answers4

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