CODEWITHSUNDEEP
iosobjective-cnsarraynspredicate
Nat
Nat

Reputation: 12942

Filter an array with other array

I've got 2 arrays:

array1 contains objects of type object1. object1 has a property id.

array2 contains objects of type object2. object2 has a property object1Id.

I know, that array2 contains objects with ids which always are in array1, but array1 can have more (or equal) objects. To show it:

Arrays

So to simplify: array1 has all objects, array2 has new objects. How to get an array with old objects..? I'm trying to do it with predicate, but it feels odd to do a loop and insert each object1Id to the predicate. Is there any other option? How to do it properly?

Upvotes: 1

Views: 155

Answers (3)

David Berry
David Berry

Reputation: 41226

NSArray*            oldIds = [array2 valueForKeyPath:@"object1Id"];
NSPredicate*        predicate = [NSPredicate predicateWithFormat:@"NOT (id IN %@)", oldIds];
NSArray*            objects = [array1 filteredArrayUsingPredicate:predicate];

Upvotes: 0

Rafał Sroka
Rafał Sroka

Reputation: 40030

It looks like you are trying to perform a set operations. What can be helpful is NSMutableSet class. Use setWithArray to create sets. Then use methods like:

  • unionSet:
  • minusSet:
  • intersectSet:
  • setSet:

To get subsets that match your criteria.

Source: NSMutableSet Class Reference

Hope it helps.

Upvotes: 1

Wain
Wain

Reputation: 119021

You can use a predicate, and you don't need a loop if you use KVC.

Get the array of ids that should be excluded:

NSArray *excludeIds = [array2 valueForKey@"object1Id"];

Create the predicate:

NSPredicate *filterPredicate = [NSPredicate predicateWithFormat:@"NOT (id IN %@)", excludeIds];

Then filter:

NSArray *oldObjects = [array1 filteredArrayUsingPredicate:filterPredicate];

Upvotes: 3

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