Question

I have an NSArray formed with objects of a custom class. The class has 3 (city, state, zip) string properties. I would like to get all unique state values from the array.

I did read through the NSPredicate class but couldn’t make much of how to use it in this case. The only examples I could find were for string operations.

Can someone please help me out?

Answer 1

The totally simple one liner:

NSSet *uniqueStates = [NSSet setWithArray:[myArrayOfCustomObjects valueForKey:@"state"]];

The trick is the valueForKey: method of NSArray. That will iterate through your array (myArrayOfCustomObjects), call the -state method on each object, and build an array of the results. We then create an NSSet with the resulting array of states to remove duplicates.

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Starting with iOS 5 and OS X 10.7, there’s a new class that can do this as well: NSOrderedSet. The advantage of an ordered set is that it will remove any duplicates, but also maintain relative order.

NSArray *states = [myArrayOfCustomObjects valueForKey:@"state"];
NSOrderedSet *orderedSet = [NSOrderedSet orderedSetWithArray:states];
NSSet *uniqueStates = [orderedSet set];