When is it better to use an NSSet over an NSArray?

Question

I have used NSSets many times in my apps, but I have never created one myself.

When is it better to use an NSSet as opposed to an NSArray and why?

Answer 1

Just to add a bit of it i use set sometimes just to remove duplicates from array like :-

NSMutableSet *set=[[NSMutableSet alloc]initWithArray:duplicateValueArray]; // will remove all the duplicate values