Question

I’m attempting to cull my NSMutableArray of elements with filterUsingPredicate.

The tricky part is that I always want to keep at least 10 items in the array, regardless if whether they pass the predicate test. So something like:

NSPredicate * cullPredicate = [NSPredicate predicateWithFormat:
        @"distanceFromCurrent <= 25 OR index < 10"];

[self.myArray filterUsingPredicate:cullPredicate];

The ‘OR index < 10’ as an indication of what I’d like to do… I realize it won’t work.

Is this possible with predicates? Or do I need to pull out another array with elements starting at 10, apply the filter, and then add it back onto the original array?

Answer 1

NSPredicate has a -predicateWithBlock: method that you can use to do this. Something like this:

NSArray *array = [[self.myArray copy] autorelease];
NSPredicate *predicate = [NSPredicate predicateWithBlock:^BOOL(id evaluatedObject, NSDictionary *bindings) {        
    if ([array indexOfObject:evaluatedObject] < 10) return YES;
    return evaluatedObject.distanceFromCurrent <= 25;
}];
[self.myArray filterUsingPredicate:predicate];