Question

Is it possible to use aggregate operator such as @min inside a predicate?

BTW The predicate filters an array of objects.

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"ANY SELF.score == @min.score"];

I know you can retrieve the min value using the key-value operators eg:

NSNumber *minScore = [myArray valueForKeyPath:@"@min.score"];

So far I only get errors about the objects not being key value compliant for “@min”.

Thanks

Answer 1

The reason that you’re getting that error is that the predicate is being applied to each object in myArray, and those objects apparently don’t support the key path @min.score. NSPredicate does have support for at least some of the collection operators, though. Here’s a simple example that works:

NSDictionary *d1 = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:35] forKey:@"score"];
NSDictionary *d2 = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:52] forKey:@"score"];
NSDictionary *d3 = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:13] forKey:@"score"];
NSDictionary *d4 = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:19] forKey:@"score"];
NSArray *array = [NSArray arrayWithObjects:d1, d2, d3, d4, nil];

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF.score == %@[e-mail]", array];
NSLog(@"Min dictionaries: %@", [array filteredArrayUsingPredicate:predicate]);

You can see that in this case, the @min.score key path is applied to the array, which makes sense. The output is an array containing the one dictionary that contains the minimum value:

Min dictionaries: (
        {
        score = 13;
    }
)