Question

I’m trying to store arrays of objects in an Mutable Dictionary, but it seems like the dictionary is losing some of my arrays (or maybe the arrays are losing the data?).

Anyways, here’s where I’m at:

- (NSDictionary *)getTicketsByDay:(NSArray *)tickets {
    // take an array of tickets and return a dictionary with dates (given by
    // NSDateFormatterShortStyle) as keys and arrays of tickets as the values

    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setDateStyle:NSDateFormatterShortStyle];

    // get NSDate object without time (only month, day, year)
    unsigned int flags = NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit;
    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSMutableDictionary *datesDict = [[NSMutableDictionary alloc] init];

   for (Ticket *ticket in tickets) {
        NSDateComponents *ticketDateNoTimeComponents = [calendar components:flags fromDate:[ticket createdAt]];
        NSDate *ticketDateNoTime = [calendar dateFromComponents:ticketDateNoTimeComponents];
        NSString *dateString = [formatter stringFromDate:ticketDateNoTime];
        NSMutableArray *ticketArray = [datesDict objectForKey:dateString];
        NSLog(@"%lu", [ticketArray count]);
        if (ticketArray == nil) {
            NSLog(@"it's here: %@", dateString);
            ticketArray = [[NSMutableArray alloc] init];
        }
        [ticketArray addObject:ticket];
        NSLog(@"%lu", [ticketArray count]);
        [datesDict setObject:ticketArray forKey:dateString];
     }
     return datesDict;
}

But then on the console, at random places (although the same places every time), I get something like

41
41
42
0
it's here: 6/29/12
1

even though the key for the previous objects was also “6/29/12”. I’ve also had it print all the keys in the dictionary and there is only 1.

So somewhere I’m losing my data. What’s going on?

I should also mention that I’m on 10.7.4 and using ARC.

Answer 1

The code looks fine to me (if you include suggestions from @ConradShultz)

Note that you don’t need to create the ticketDateNoTime since you’re using a date format, it will always generate the short format string even if the date contains a time…

So your code could be simplified to:

- (NSDictionary *)getTicketsByDay:(NSArray *)tickets {
    // take an array of tickets and return a dictionary with dates (given by
    // NSDateFormatterShortStyle) as keys and arrays of tickets as the values

    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setDateStyle:NSDateFormatterShortStyle];

    NSMutableDictionary *datesDict = [[NSMutableDictionary alloc] init];

    for (Ticket *ticket in tickets) {
        NSString *dateString = [formatter stringFromDate:[ticket createdAt]];
        NSMutableArray *ticketArray = [datesDict objectForKey:dateString];
        NSLog(@"%lu", [ticketArray count]);
        if (ticketArray == nil) {
           NSLog(@"it's here: %@", dateString);
            ticketArray = [[NSMutableArray alloc] init];
            [datesDict setObject:ticketArray forKey:dateString];
        }
        [ticketArray addObject:ticket];
        NSLog(@"%lu", [ticketArray count]);
    }
    return datesDict;
}