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Editorial Team
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Asked: 2026-06-18T01:27:50+00:00

Is there a way to rearrange an array of objects such that the contents

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Is there a way to rearrange an array of objects such that the contents are rearranged such that all the xth elements are grouped in another array? I’m not sure the best way to explain this so I’ll illustrate with an example:

theArray has 5 properties: number, color, size, height, quality. There are 50 instances of this array, each with different properties.

I want to rearrange this so there are 5 arrays with 50 items inside each array.

The way I would do it is:

NSMutableArray *innerTemp = [[NSMutableArray alloc] initWithCapacity:49];
NSMutableArray *outerTemp = [[NSMutableArray alloc] initWithCapacity:4];

for (int i = 0 ; i < [theArray count]; i++){
    [innerTemp addObject:[[theArray objectAtIndex:i] number]];
    [innerTemp addObject:[[theArray objectAtIndex:i] color]];
    [innerTemp addObject:[[theArray objectAtIndex:i] height]];
    [innerTemp addObject:[[theArray objectAtIndex:i] age]];
    [innerTemp addObject:[[theArray objectAtIndex:i] quality]];

    [outerTemp addObject:temp];
}

So I guess my question is, is there some easier way/more efficient to do this?

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1 Answer

  1. Editorial Team

    Just use KVC (Key Value Coding):

    Assuming your class looks something like this:

    @interface InstanceClass : NSObject

// IIRC properties need to be objects (hence the NSValue around NSSize), there is no auto-wrapping.
@property (readwrite, strong, nonatomic) NSNumber *number;
@property (readwrite, strong, nonatomic) NSColor *color;
@property (readwrite, strong, nonatomic) NSValue *sizeValue;
@property (readwrite, strong, nonatomic) NSNumber *height;
@property (readwrite, strong, nonatomic) NSNumber *quality;

@end

    and you have an array like 

    NSArray *instances = @[instance1, instance2, instance3, instance4, ...];

    then this would be all you need:

    NSArray *numbers   = [instances valueForKey:@"number"];  // array of numbers.
NSArray *colors    = [instances valueForKey:@"color"];   // array of colors.
NSArray *sizes     = [instances valueForKey:@"size"];    // array of sizes.
NSArray *heights   = [instances valueForKey:@"height"];  // array of heights.
NSArray *qualities = [instances valueForKey:@"quality"]; // array of qualities.

    This will do the trick.

    Assuming your items in the instances array are numbered from 1..n a call to [instances valueForKey:@"number"] would then return an NSArray like @[@1, @2, @3, @4, ...].

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