NSArray group by

NSArray+Extensions

- (NSDictionary *)groupByKey:(NSString *)key
{
    NSMutableDictionary *dictionary = [NSMutableDictionary dictionary];
    
    for (id obj in self) {
        id keyValue = [obj valueForKey:key];
        if (keyValue) {
            NSMutableArray *array = dictionary[keyValue];
            if (!array) {
                array = [NSMutableArray array];
                dictionary[keyValue] = array;
            }
            [array addObject:obj];
        }
    }
    return [dictionary copy];
}