Filter an array with other array

Question

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?

Wain · Accepted Answer · 2014-02-26 23:47:04Z

3

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];

answered Feb 26, 2014 at 23:47

Wain

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Comments

Rafał Sroka · Accepted Answer · 2014-02-26 23:47:19Z

1

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.

answered Feb 26, 2014 at 23:47

Rafał Sroka

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1 Comment

Wain Over a year ago

This approach is generally more suited to arrays / collections containing the same type of object

David Berry · Accepted Answer · 2014-02-26 23:50:15Z

0

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

answered Feb 26, 2014 at 23:50

David Berry

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