shuffle NSMutableArray category

NSMutableArray+Shuffling.h

@interface NSMutableArray (Shuffling)
- (void)shuffle;
@end

NSMutableArray+Shuffling.m

#import "NSMutableArray+Shuffling.h"

@implementation NSMutableArray (Shuffling)

- (void)shuffle
{
    NSUInteger count = [self count];
    for (NSUInteger i = 0; i < count; ++i) {
        // Select a random element between i and end of array to swap with.
        NSInteger nElements = count - i;
        NSInteger n = arc4random_uniform(nElements) + i;
        [self exchangeObjectAtIndex:i withObjectAtIndex:n];
    }
}

@end

Extracted from http://stackoverflow.com/questions/56648/whats-the-best-way-to-shuffle-an-nsmutablearray