Similar to HashSet in iPhone

Question

I am java programmer. There is concept of HashSet in Java that don't add duplicate elements in a Set. What is the similar concept in iPhone that do same ?

Please hint.

Thanks in advance.

Most collection classes of the Foundation framework are described in detail in the ["Collections Programming Topics"](https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/Collections/Collections.html) documentation. If order is relevant then you can use NS(Mutable)OrderedSet. — Martin R, Aug 25 '14 at 11:57

score 1 · Accepted Answer · answered Aug 25 '14 at 11:49

You can use NSSet in iOS. NSSet is a (unordered) collection of unique items. So, you can find the unique items in your array like so:

     NSSet *uniqueElements = [NSSet setWithArray:myArray];

    // iterate over the unique items
    for(id element in uniqueElements)
       {
          // do something
       }

NSSet most likely uses a hash algorithm to make insertion O(1) (compared to O(n^2) to check if each item is unique by iteration), but the Apple documentation does not make such a guarantee so you probably shouldn't count on that implementation detail.

If, for some reason you need to keep the unique items in a sorted (ordered) collection, you can turn the set back into an array with -[NSSet allObjects] and then sort the resulting array.

I want they should be in same order as I insert into it. Does NSSet will be helpful for that ? — N Sharma, Aug 25 '14 at 11:52
If you want it to be in same order then use NSOrderedSet: It is the ordered collection of distinct objects. — Utkarsha, Aug 25 '14 at 11:58

rckoenes · Answer 2 · 2014-08-25T11:25:48.943

0

NSSet use the has of NSObject to make sure that there are not duplicates.

Or NSMutableSet if you need to add thing to the set.

edited Aug 25 '14 at 11:25

answered Aug 25 '14 at 11:13

rckoenes

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so I use `NSSet`, will it be helpful to achieve my requirement ? – N Sharma Aug 25 '14 at 11:14
Since I'm not familiar with java I can't confirm that they are 100% the same. But `NSSet` does doe what you descripted. – rckoenes Aug 25 '14 at 11:17
From the documentation it seems that `NSSet` is immutable. That would make it fundamentally different from `HashSet` in Java, and probably wouldn't do what is required. – gandaliter Aug 25 '14 at 11:24
That is how Objective-C work, just use `NSMutableSet`. – rckoenes Aug 25 '14 at 11:25

score 0 · Answer 3 · answered Aug 25 '14 at 11:21

0

HashSet is the Java implementation of a Hash Table. NSHashTable is, I believe, the Cocoa equivalent.

answered Aug 25 '14 at 11:21

gandaliter

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Similar to HashSet in iPhone

3 Answers3