I've tried that, but once you pass in blocks as arguments, the whole thing becomes a lot harder to read. I have no clue how to indent

    [[array filter:^BOOL (id obj) {
            return [obj passesTest];
        }]
        map:^id (id obj) {
            return [obj transformedObject]
        }];

Edit: Also, it's good practice to prefix your categories methods so they don't clash with other category's, so you'd have something like us_map:, us_filter:, reducing readability even further.