objective c - Filter NSArray of custom objects

Question

I have a NSArray of Contact objects, we can call it contacts. Contact is a superclass, FacebookGroup and Individual are subclasses of Contact. FacebookGroup has a property called individuals which is a set of Individual objects.

I also have a NSArray of NSString objects, we can call it userIDs.

What I want to do is create a new NSArray from the existing contacts array that match the userIDs in userIDs.

So if contacts has 3 Contact objects with userID 1,2 and 3. And my userIDs has a NSString object 3. Then I want the resulting array to contain Contact which equals userID 3.

Contact.h

Contact : NSObject

FacebookGroup.h

FacebookGroup : Contact

@property (nonatomic, strong) NSSet *individuals;

Individual.h

Individual : Contact

@property (nonatomic, strong) NSString *userID;

Answer 1

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"userId = %@", myContact.userId];
NSArray *filteredArray = [contacts filteredArrayUsingPredicate:predicate];