Extension to the NSMutableArray class to provide randomization functions

NSMutableArray+Random.h

#import <Foundation/Foundation.h>

@interface NSMutableArray (WSRandom)


- (id) objectAtRandomIndex;

- (void) shuffle;


@end

NSMutableArray+Random.m

#import "NSMutableArray+WSRandom.h"


@implementation NSMutableArray (WSRandom)

- (id) objectAtRandomIndex
{
    
    switch (self.count)
    {
        case 0:
            return nil;
            break;
            
        case 1:
            return self.firstObject;
            break;
            
        default:
            return self[arc4random_uniform((u_int32_t)self.count)];
            break;
    }
    
}

- (id) popAtRandomIndex
{
    id obj = [self objectAtRandomIndex];
    if(obj)
    {
        [self removeObject:obj];
    }
    
    return obj;
}

- (void) shuffle
{
    
    // Fisher–Yates shuffle
    
    NSUInteger i = self.count;
    
    if(i < 2)
    {
        return;
    }
    
    while (i > 1)
    {
        i--;
        NSUInteger j = arc4random_uniform((u_int32_t)i);
        [self exchangeObjectAtIndex:i withObjectAtIndex:j];
    }
    
}

@end