current community

your communities

more stack exchange communities

Stack Exchange
tour help
careers 2.0
Take the 2-minute tour ×
Stack Overflow is a question and answer site for professional and enthusiast programmers. It's 100% free, no registration required.
up vote 1 down vote favorite
1

I'm quite confused on how to add objects in multidimensional arrays.

Is initializing multidimensional arrays are the same with just a simple array?

This is my initialization.

testList = [[NSMutableArray alloc] init];

I need to do something like

testList[i][j] = item;

i tried

[[[testList objectAtIndex:i]objectAtIndex:j] addObject:item];

but it doesn't seem to work :(

share|improve this question
    
you should add more NSMutableArray (or NSArray) objects to your original testList, because there is no multi dimension array in objective-c; you could use the NSMutableDictionary (or NSDictionary) with KVC; or you could combined them with each other; or you could use NSMutableSet (or NSSet) or you could combine everything with everything... everything is highly limitless, it depends on what kind of data you'd like to represent. –  holex Jul 17 '12 at 16:10

4 Answers 4

up vote 3 down vote accepted

You are add to much C to do this. This is important to know how to NSMutableArray works and how it's different compare to 2D arrays known from C/C++.

In mutable array you could store another arrays. For example:

NSMutableArray *first = [NSMutableArray alloc] init];
NSMutableArray *second = [NSMutableArray alloc] init];

[first addObject:second];

Now you have array in first row in first array! This is something very like C/C++ 2D arrays.

So if you want to add some object "to 0,0" you do this:

NSString *mytest = [NSString alloc] initWithString:@"test"];
[second addObject:mytest];
[first addObject:second];

So now your second contains NSStrings and first contains second. Now you can loop this like you want.

----EDIT: IF you want 1,0 you simply need another instance of second NSMutableArray. For example you have this array:

arr

So here you will be have 3 elements in second array.

NSMutableArray *first = [NSMutableArray alloc] init];
for(int i =0 ; i < your_size_condition ; i++) {//if you have size, if don't not a problem, you could use while!
   NSArray *second = [[NSArray alloc] initWithObjects:"@something",@"somethingelse",@"more",nil];
   [first addObject:second];
}

You may want to implement NSCopying protocol to do this.

share|improve this answer
    
hmm, i think i got what you mean, but then what if i want to add at 1,0? –  Rowie Po Jul 17 '12 at 10:37
    
i update my answer. Hope i made it clear. –  Kuba Jul 17 '12 at 10:50
    
solved it! thanks man! –  Rowie Po Jul 18 '12 at 3:56
up vote 3 down vote

If you need a fixed size array, then use plain C array. Before using dynamic ObjC array it needs to create it:

NSMutableArray* array = [NSMutableArray arrayWithCapacity:N];
for(int i=0; i<N; i++) {
    [array addObject:[NSMutableArray arrayWithCapacity:M]];
}

UPD: The following methods might be helpful to work with such array:

[[array objectAtIndex:i] addObject:obj];
[[array objectAtIndex:i] insertObject:obj atIndex:j];
[[array objectAtIndex:i] replaceObjectAtIndex:j withObject:obj];
share|improve this answer
    
nope, the sizes are dynamic, i just need to know how to add objects in something like testList[i][n] –  Rowie Po Jul 17 '12 at 10:32
    
in NSMutableArray you don't have to declare size first, you simply add another object. There is more like lists in c++ than arrays. –  Kuba Jul 17 '12 at 10:34
up vote 0 down vote

To expand upon @onegray's answer, you can set up some category methods to make soft multidimensional arrays easier to deal with.

MultiMutableArray.h

@interface NSMutableArray(MultiMutableArray)
  -(id)objectAtIndex:(int)i subIndex:(int)s;
  -(void)addObject:(id)o toIndex:(int)i;
@end


@implementation NSMutableArray(MultiMutableArray)

MultiMutableArray.m

#import "MultiMutableArray.h"

-(id)objectAtIndex:(int)i subIndex:(int)s
{
    id subArray = [self objectAtIndex:i];
    return [subArray isKindOfClass:NSArray.class] ? [subArray objectAtIndex:s] : nil;
}

-(void)addObject:(id)o toIndex:(int)i
{
    while(self.count <= i)
        [self addObject:NSMutableArray.new];
    NSMutableArray* subArray = [self objectAtIndex:i];
    [subArray addObject: o];
}

@end

example, MultiArrayTests.m

#import <SenTestingKit/SenTestingKit.h>

#import "MultiMutableArray.h"

@interface MultiArrayTests : SenTestCase
@end

@implementation MultiArrayTests

-(void)testMultiArray
{
    NSMutableArray* a = NSMutableArray.new;
    [a addObject:@"0a" toIndex:0];
    [a addObject:@"0b" toIndex:0];
    [a addObject:@"0c" toIndex:0];
    [a addObject:@"1a" toIndex:1];
    [a addObject:@"1b" toIndex:1];
    [a addObject:@"2a" toIndex:2];
    STAssertEquals(a.count, 3U, nil);
    NSMutableArray* a1 = [a objectAtIndex:0];
    NSMutableArray* a2 = [a objectAtIndex:1];
    NSMutableArray* a3 = [a objectAtIndex:2];
    STAssertEquals(a1.count, 3U, nil);
    STAssertEquals(a2.count, 2U, nil);
    STAssertEquals(a3.count, 1U, nil);
}

@end

I have written further details at http://peterdeweese.tumblr.com/post/27411932460/soft-multi-dimensional-arrays-in-objective-c

share|improve this answer
up vote -1 down vote 
[[testList objectAtIndex:i] insertObject:item atIndex:j];
share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.