How to count number of similar objects in array

vincefried · May 2012

Hello,

let's say, I have an array like this:

1
1
1
2
2
2
2
2
3
3
3
3
3
3

and I want to count, how many "1", how many "2" and how many "3" I have in this array and save that to a new array. Like this:

3
5
6

How can I do this?

I appreciate your help :)

Greetings,
vincefried

baja_yu · May 2012

You could do this. Create a mutable set, then iterate through the array, for each item of the array try to retrieve the value for key, by using the array item as the key. If it returns nil it means your seeing that item for the first time, so add an object to the array with that key and 1 as value. If it doesn't return nil you've had that value before so take the value, increment it by one and add it back to the set. At the end you'll have a set where keys are your numbers and their values are how many times they occurred in the array.

You could also sort the array then iterate through it counting while the items are the same then displaying the result when it changes and so on.

BrianSlick · May 2012

NSCountedSet

Domele · May 2012

Didn't even know such a class existed. I have no use for it right now but I'm sure I will later, thanks Brian.

baja_yu · May 2012

BrianSlick;434754 said:
NSCountedSet

Even better! I completely skipped that one.

vincefried · May 2012

Thanks for your answers, I got it to work, but pretty complicated:


for (int i = 0; i < [indexArray count]; i++) {
        
        if ([[NSString stringWithFormat:@\"%@\", [indexArray objectAtIndex:i]] isEqualToString:@\"1\"]) {
            
            array1counted++;
            NSLog(@\"array1counted: %i\", array1counted);
            
        }    
    }

[array1 addObject: [NSString stringWithFormat:@\"%i\", array1counted]];

Maybe, I will try to use your suggestions later for a more efficient way to count. Thanks again :)

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How to count number of similar objects in array

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