Question

A quick question about NSArrays and NDictionarys.

I have and NSArray containing NSDictionarys.
The NSDictionary contain a date and a string.

What I would like to do is end up with an NSDictionary with keys dates and values arrays of strings that are on that date.

What would be the best way to do this

Answer 1

NSMutableDictionary *result = [NSMutableDictionary dictionary];
for (NSDictionary *dict in array) {
    NSDate *date = [dict objectForKey:@"dateKey"];
    NSString *string = [dict objectForKey:@"stringKey"];
    NSMutableArray *stringsWithDate = [result objectForKey:date];
    if (!stringsWithDate) {
        stringsWithDate = [NSMutableArray array];
        [result setObject:stringsWithDate forKey:date];
    }
    [stringsWithDate addObject:string];
}

Note that NSDate is not a “calendar date”, so the same day with a different time will be considered as a distinct date in your result dictionary.