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

Answer 1

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.