Check duplicate property values of objects in NSArray

Question

I have an NSArray containing objects with a size property.

How can I check if the NSArray has two objects with the same value for size?

Can I do something like:

int i = 0;
for (id item1 in myArray) {
    NSDecimalNumber *size1 = [item1 size];

    for (id item2 in myArray) {
        NSDecimalNumber *size2 = [item2 size];

        if ([size1 isEqual:size2]) {
            i ++;
        }
    }
}

if (i > [myArray count]) {
    NSLog(@"Duplicate Sizes Exist");
}

Or is there an easier way?

You can do the above, but it's "N-squared" and generally considered poor form for larger collections. — Hot Licks
– Hot Licks, Commented May 9, 2013 at 11:26

jscs · Accepted Answer · 2014-07-29 20:45:45Z

3

Try this code:

NSSet *myset = [NSSet setWithArray:[myarray valueForKey:@"size"]];
int duplicatesCount = [myarray count] - [myset count];

size here is the object property.

edited Jul 29, 2014 at 20:45

jscs

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answered May 9, 2013 at 11:59

Amar

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1 Comment

Michał Ciuba Over a year ago

You can also use KVC collection operators: [myArray valueForKeyPath:@"@distinctUnionOfObjects.size"]. More details here: nshipster.com/kvc-collection-operators

Community · Accepted Answer · 2017-05-23 12:03:26Z

1

Use NSCountedSet. then add all your objects to the counted set, and use the countForObject: method to find out how often each object appears in your array.

You can check this link also how-to-find-duplicate-values-in-arrays

Hope it helps you

edited May 23, 2017 at 12:03

CommunityBot

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answered May 9, 2013 at 11:18

Nishant Tyagi

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1 Comment

robspencer77 Over a year ago

Yeah, but the objects may be different but have the same size. So the array my have 2 objects which are size 3, but one is brown and one is grey. Your suggestion would only pick up identical objects.

Hot Licks · Accepted Answer · 2013-05-09 11:24:02Z

0

Probably simplest is to sort the array based on the size field and then step through the sorted list looking for adjacent dupes.

You could also "wrap" each object in one that exports the size as its key and use a set. But that's a lot of extra allocations.

But if you only want to know if dupes exist, and not which ones they are, create an NSNumber for each object's size and insert the NSNumbers in a set. The final size will tell you how many dupes.

answered May 9, 2013 at 11:24

Hot Licks

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1 Comment

robspencer77 Over a year ago

That's a good suggestion as the array is already sorted. Thanks Hot Licks :)

Buntylm · Accepted Answer · 2013-05-09 11:32:18Z

0

NSArray *cleanedArray = [[NSSet setWithArray:yourArraywithDuplicatesObjects ] allObjects];

Use Sets this will remove all duplicates objects.Will return NSArrayNSCountedSet and use countForObject: method to find out how often each object appears how many times.

edited May 9, 2013 at 11:32

answered May 9, 2013 at 11:20

Buntylm

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1 Comment

robspencer77 Over a year ago

I knew there would be a lot of suggestions to use NSSet, but I don't have duplicate objects, just need to check if any objects have the same propert value :)

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