Force Shuffle NSMutableArray

Question

I have a NSMutableArray called putNumberUsed. It contains the following objects @\"blah1,@\"blah2\",@\"blah3\",@\"blah4\". I want to shuffle these objects randomly so for ex

Answer 1

Here is a shuffling solution with all positions forced to change when count > 1.

Add a category like NSMutableArray+Shuffle.m:

@implementation NSMutableArray (Shuffle)
// Fisher-Yates shuffle variation with all positions forced to change
- (void)unstableShuffle
{
    for (NSInteger i = self.count - 1; i > 0; i--)
        // note: we use u_int32_t because `arc4random_uniform` doesn't support int64
        [self exchangeObjectAtIndex:i withObjectAtIndex:arc4random_uniform((u_int32_t)i)];
}
@end

Then you can shuffle like:

[putNumbersUsed unstableShuffle];

This solution:

• has no modulo bias
• has no naive bias
• has no sorting bias

A Swift 3.2 and Swift 4 equivalent is:

extension Array {
    mutating func unstableShuffle() {
        for i in stride(from: count - 1, to: 0, by: -1) {
            swapAt(i, Int(arc4random_uniform(UInt32(i))))
        }
    }
}

A Swift 3.0 and 3.1 equivalent is:

extension Array {
    mutating func unstableShuffle() {
        for i in stride(from: count - 1, to: 0, by: -1) {
            swap(&self[i], &self[Int(arc4random_uniform(UInt32(i)))])
        }
    }
}

Note: An algorithm for regular shuffling (where a result with same positions being possible) is also available

Answer 2

generate a random number for index

int randomInt = arc4random() % [putNumberUsed count];
[putNumberUsed objectAtIndex:randomInt];

Answer 3

Use this:

for (int i = 0; i < [putNumberUsed count]; i++) {
    int random = arc4random() % [putNumberUsed count]; 
    [putNumbersUsed exchangeObjectAtIndex:random withObjectAtIndex:i]; 
}

Answer 4

You can shuffle the object by using the following line of code,

[putNumbersUsed exchangeObjectAtIndex:3 withObjectAtIndex:0];

I think this may useful to you.

Answer 5

I think, You can write a loop for that. Please check the following code,

for (int i = 0; i < putNumberUsed.count; i++) {
    int randomInt1 = arc4random() % [putNumberUsed count];
    int randomInt2 = arc4random() % [putNumberUsed count];
    [putNumberUsed exchangeObjectAtIndex:randomInt1 withObjectAtIndex:randomInt2];
}

I this this may be useful to you.

Answer 6

From iOS 10.x++ new concept of shuffle array is given by Apple,

You need to import the framework :

ObjeC

#import <GameplayKit/GameplayKit.h>

NSArray *shuffledArray = [yourArray shuffledArray];

Swift

import GameplayKit

let shuffledArray = yourArray.shuffled()