Using NSSet vs NSDictionary

Question

I understand that there is a difference in how elements are stored in a NSSet and a NSDictionary, https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/Collections/Collections.html

But from a development point of view, when should I use NSSet vs NSDictionary? The time complexity for both is O(1)

Edit: I came across the question - Remove duplicates from an array. One solution stored the elements in a NSDictionary to remove duplicates, the other solution stored the elements in a NSSet.

I was wondering which would be a better approach

Answer 1

NSSet and NSDictionary are very different. NSSet is a set of elements meanwhile NSDictionary keeps a list of key-value pairs, so you can access the Value directly when you have the Key. It's more meaningful to compare NSSet to NSArray than to NSDictionary.