Question

I have an NSArray and I’d like to create a new NSArray with objects from the original array that meet certain criteria. The criteria is decided by a function that returns a BOOL.

I can create an NSMutableArray, iterate through the source array and copy over the objects that the filter function accepts and then create an immutable version of it.

Is there a better way?

Answer 1

NSArray and NSMutableArray provide methods to filter array contents. NSArray provides filteredArrayUsingPredicate: which returns a new array containing objects in the receiver that match the specified predicate. NSMutableArray adds filterUsingPredicate: which evaluates the receiver’s content against the specified predicate and leaves only objects that match. These methods are illustrated in the following example.

NSMutableArray *array =     [NSMutableArray arrayWithObjects:@'Bill', @'Ben', @'Chris', @'Melissa', nil];  NSPredicate *bPredicate =     [NSPredicate predicateWithFormat:@'SELF beginswith[c] 'b'']; NSArray *beginWithB =     [array filteredArrayUsingPredicate:bPredicate]; // beginWithB contains { @'Bill', @'Ben' }.  NSPredicate *sPredicate =     [NSPredicate predicateWithFormat:@'SELF contains[c] 's'']; [array filteredArrayUsingPredicate:sPredicate]; // array now contains { @'Chris', @'Melissa' }