Grouping of Custom Objects in Objective-C

Question

I have and array of custom objects of Person Class

Person : NSObject{
    NSString *firstName;
    NSString *lastName; 
    NSString *age;
}

NSMutableArray          


        

Answer 1

- (NSDictionary *)groupObjectsInArray:(NSArray *)array byKey:(id  (^)(id item))keyForItemBlock
{
    NSMutableDictionary *groupedItems = [NSMutableDictionary new];
    for (id item in array)
    {
        id  key = keyForItemBlock(item);
        NSParameterAssert(key);

        NSMutableArray *arrayForKey = groupedItems[key];
        if (arrayForKey == nil)
        {
            arrayForKey = [NSMutableArray new];
            groupedItems[key] = arrayForKey;
        }
        [arrayForKey addObject:item];
    }
    return groupedItems;
}