Neat snippet to group objects in an NSArray based on equal values under a given keypath.

nsarray_group.m

@implementation NSArray (GroupBy)

- (NSArray *)groupByKeyPath:(NSString *)keyPath {
    NSArray *distinctValues = [self valueForKeyPath:[@"@distinctUnionOfObjects." stringByAppendingString:keyPath]];
    NSMutableArray *result = [NSMutableArray arrayWithCapacity:[distinctValues count]];
    
    for (id groupValue in distinctValues) {
        NSString *predicateFormat = [NSString stringWithFormat:@"(%@ == %%@)", keyPath];
        NSPredicate *predicate = [NSPredicate predicateWithFormat:predicateFormat, groupValue];
        NSArray *group = [self filteredArrayUsingPredicate:predicate];
        [result addObject:group];
    }
    
    return result;
}

@end