Question

I have an array of categories, and another array of category IDs. I want to pull out the categories with matching IDs. At the moment, my code looks a bit like this:

- (NSArray *)categoriesFromArray:(NSArray *)categories withIDs:(NSArray *)categoryIDs {
    NSMutableArray *categoriesWithIDs = [NSMutableArray array];

    for (SGBCategory *category in categories) {
        for (NSNumber *categoryID in categoryIDs) {
            if ([category.categoryID isEqual:categoryID]) {
                [categoriesWithIDs addObject:category];
                break;
            }
        }
    }

    return categoriesWithIDs;
}

Ewww, I know. So what I’d like to do is something like SELECT * FROM categories WHERE categories.categoryID in (categoryIDs) does in SQL. I think NSPredicate is the objective-c way of expressing that sort of thing, but I don’t know how to get it to do what I want. How can I speed up my array search with an NSPredicate?

Answer 1

return [categories filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"categoryID IN %@", categoryIDs]];

I don’t know that it will be any faster, though. It basically has to do the same sort of thing as your code, plus build a predicate.

You can improve your code by making an NSSet from the categoryIDs and using -containsObject: instead of looping over the categoryIDs and calling -isEqual: manually.