How can I randomly rearrange data in multiple corresponding NSMutableArrays?

Question

I have an array with images of animals, another array with the corresponding animal's sound and the last one with the animal's name. for example:

imagesArray:

0: [UIImage imageNamed:@"Elephant.png"]
1: [UIImage imageNamed:@"Dog.png"]
2: [UIImage imageNamed:@"Cat.png"]

soundsArray:

0: Elephant.mp3
1: Dog.mp3
2: Cat.mp3

wordsArray:

0: Elephant
1: Dog
2: Cat

They are sync and work together with the same counter. I want at start to arrange them randomly in new 3 arrays, but I want the same animal details (image or sound or word) to be the same in all 3 arrays. For example, the new arrays should look like this:

imagesArray:

0: [UIImage imageNamed:@"Cat.png"]
1: [UIImage imageNamed:@"Dog.png"]
2: [UIImage imageNamed:@"Elephant.png"]

soundsArray:

0: Cat.mp3
1: Dog.mp3
2: Elephant.mp3

wordsArray:

0: Cat
1: Dog
2: Elephant

I wrote this code to the view did load:

theNewAnimalsPicture = [NSArray arrayWithObjects:[UIImage imageNamed:@"Square_Bee.png"],[UIImage imageNamed:@"Square_Bird.png"],[UIImage imageNamed:@"Square_Cat.png"],[UIImage imageNamed:@"Square_Chicken.png"],[UIImage imageNamed:@"Square_Cow.png"],[UIImage imageNamed:@"Square_Dog.png"],[UIImage imageNamed:@"Square_Elephant.png"],[UIImage imageNamed:@"Square_Frog.png"],[UIImage imageNamed:@"Square_Horse.png"],[UIImage imageNamed:@"Square_Lion.png"],[UIImage imageNamed:@"Square_Monkey.png"],[UIImage imageNamed:@"Square_Sheep.png"], nil];
theNewAnimalsSound = [NSArray arrayWithObjects:@"Bee.mp3",@"Bird.mp3",@"Miao.mp3",@"Chicken.mp3",@"Cow.mp3",@"Waff.mp3",@"Elephant2.mp3",@"Frog.mp3",@"Horse.mp3",@"LionSound.mp3",@"Monkey_Sound.mp3",@"Sheep.mp3", nil];
theNewAnimalsWord = [NSArray arrayWithObjects:@"Bee",@"Bird",@"Cat",@"Chicken",@"Cow",@"Dog",@"Elephant",@"Frog",@"Horse",@"Lion",@"Monkey",@"Sheep", nil];

for (int i =0;i<[theNewAnimalsPicture count];i++)
{
    int number = arc4random() % [theNewAnimalsPicture count];
    [PicturesAnimalArray addObject:[theNewAnimalsPicture objectAtIndex:number]];
    [SoundsAnimalArray addObject:[theNewAnimalsSound objectAtIndex:number]];
    [wordAnimalArray addObject:[theNewAnimalsWord objectAtIndex:number]];
    [theNewAnimalsPicture removeObjectAtIndex:number];
    [theNewAnimalsSound removeObjectAtIndex:number];
    [theNewAnimalsWord removeObjectAtIndex:number];
}

It isn't working. Why is that, and how can I do this in more efficient way than what I did here?

That should work I think, can you provide the error you're getting, or the output of the 3 new arrays? — Tom H, May 14 '12 at 19:57
Is this an exercise to better understand arrays or are you needing this to work for your project? If it's the latter I would recommend making an Animal object, that has the picture sound and word as properties and then only having one array! — Mike, May 14 '12 at 20:07
I actually need this, but I just finished studie. and yeah, to create an object of animal its better of course. — ytpm, May 15 '12 at 04:13

score 3 · Accepted Answer · edited Jun 20 '20 at 09:12

The best thing to do here is to create a class that encapsulates one word, sound and picture.

Animal.h

@interface Animal : NSObject
{
}

@property (nonatomic, retain) UIImage *picture;
@property (nonatomic, copy) NSString *word;
@property (nonatomic, copy) NSString *soundFile;

+ animalWithPicture:(UIImage *) aPicture word:(NSString *) aWord soundFile:(NSString *) aSoundFile;
- initWithPicture:(UIImage *) aPicture word:(NSString *) aWord soundFile:(NSString *) aSoundFile;

@end

Animal.m

#import "Animal.h"

@implementation Animal
@synthesize picture = _picture;
@synthesize word = _word;
@synthesize soundFile = _soundFile;

+ animalWithPicture:(UIImage *) aPicture word:(NSString *) aWord soundFile:(NSString *) aSoundFile
{
    return [[[self alloc] initWithPicture:aPicture word:aWord soundFile:aSoundFile] autorelease];
}

- initWithPicture:(UIImage *) aPicture word:(NSString *) aWord soundFile:(NSString *) aSoundFile
{
    self = [super init];
    if (!self) return nil;
    
    // WARNING, make sure you understand the side effects of using
    // the property accessor methods during "init" and "dealloc".
    // In this case, there should be no issue.
    
    self.picture = aPicture;
    self.word = aWord;
    self.soundFile = aSoundFile;
    
    return self;
}

- (void) dealloc
{
    self.picture = nil;
    self.word = nil;
    self.soundFile = nil;
    [super dealloc];
}

@end

Then, you could simply have a single array to contain each animal object. Consider also storing your animal information in a plist file rather than hard-coding the values like I have done here:

NSMutableArray *animals = [NSMutableArray array];

[animals addObject:[Animal animalWithPicture:[UIImage imageNamed:@"Square_Bee.png"] word:@"Bee" soundFile:@"Bee.mp3"]];
// ... etc ...
[animals addObject:[Animal animalWithPicture:[UIImage imageNamed:@"Square_Sheep.png"] word:@"Sheep" soundFile:@"Sheep.mp3"]];

For information about why using accessor methods in init and dealloc, see this answer.

score 1 · Answer 2 · answered May 14 '12 at 20:38

Another way you could do it is Create a new object, something like 'Animal'. The Animal object which would have three properties: picture, sound, name.

You could then use a single array and add the animal object to the array. Then iterate over the array.

score 1 · Answer 3 · edited May 23 '17 at 10:09

I would not store image data in the array directly. Instead you can store the image file name.
When you remove object from array, it re-indexed.

You can use a NSDictionary to store your image file name, sound file name, and word combination set.

Sample code:

#define kImageFileName   @"ImageFileName"
#define kSoundFileName     @"SoundFileName"
#define kWord           @"Word" 


NSDictionary *animalRecord = [[NSDictionary alloc]initWithObjectsAndKeys:
                              @"Square_Bee.png", kImageFileName,
                              @"bee.mp3", kSoundFileName,
                              @"Bee", kWord,                              
                              nil];

NSMutableArray *myArray = [[NSMutableArray alloc]init];
[myArray addObject:animalRecord];
// you would need to create some kind of loop and create animalRecord and add it to your myArray for all your picture/sound/word comnination sets.


//To retreive each record
int i = 0; // for example
NSString *imageFileName = [[myArray objectAtIndex:i] objectForKey:kImageFileName];  //with the filename, you can can the image whenever you need
NSString *soundFileName = [[myArray objectAtIndex:i] objectForKey:kSoundFileName];
NSString *word  = [[myArray objectAtIndex:i] objectForKey:kWord];

//to rearrange myArray's objects in random order, try this


 // This piece of code is from this [SO][1]
NSUInteger count = myArray.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;
    [myArray exchangeObjectAtIndex:i withObjectAtIndex:n];
}

Link to array rearrangement SO

There's nothing wrong with storing the image in the array. Caching and swapping will ensure that the application won't use any more memory than it has to. — dreamlax, May 15 '12 at 06:09

How can I randomly rearrange data in multiple corresponding NSMutableArrays?

3 Answers3

Animal.h

Animal.m