Sorting NSArray which contain array of dictionaries - Sort as per "Date" key

Question

I have the following NSArray which contains a dictionary at each index , here is the content, just providing first 3 records-

[
            {

                "postDate": "4/11/2011 2:03:33 PM",
                "imageLink": "",
                "eventLink": "www.google.com"
            },
            {

                "postDate": "6/16/2011 1:42:45 PM",
                "imageLink": "",
                "eventLink": "www.google.com"
            },
            {

                "postDate": "9/21/2011 10:22:34 AM",
                "imageLink": "",
                "eventLink": "www.google.com"
            }
]

NOTE:- postDate is just a NSString it is not coming in NSDate type, but I have to perform sort on basis of this key.

My task is to sort the array as per the "postDate" key , means the whole array will be sorted in order by date (ascending/descending).

I have used the following code, but didn't help as arr is storing the all the data from arrEventsData but sorting is not happening:-

NSSortDescriptor *descriptor = [[NSSortDescriptor alloc] initWithKey:@"postDate"  ascending:YES];

    NSMutableArray *arr = [[arrEventsData sortedArrayUsingDescriptors:[NSArray arrayWithObjects:descriptor,nil]]mutableCopy];

Any idea or solution will help.

Thanks

Yes, they are strings.I cannot change it as it is coming from backend. — Vizllx, May 27 '15 at 10:29
I mean I can change it manually just by updating postDate key value to Nsdate format in my program, but cannot change it from server end. — Vizllx, May 27 '15 at 10:32
What is happening to this data afterwards? Are you creating objects out of it? Or just using it like it is? — Jasper, May 27 '15 at 10:34
I want to sort the Original array and store it in other array, so that I can display events as per date range @JasperPol — Vizllx, May 27 '15 at 10:38
@Droppy I have already tried by updating the postDate key value to NSDate type, but sortedArrayUsingDescriptors doesn't work. — Vizllx, May 27 '15 at 10:41

score 4 · Accepted Answer · answered May 27 '15 at 10:47

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"M/dd/yyyy H:mm:ss a"];

NSArray *sortedByDates = [arr sortedArrayUsingComparator:^NSComparisonResult(NSDictionary *obj1, NSDictionary *obj2)
{
    NSDate *date1 = [dateFormatter dateFromString:obj1[@"postDate"]];
    NSDate *date2 = [dateFormatter dateFromString:obj2[@"postDate"]];
    return [date1 compare:date2];
}];
NSLog(@"Sorted Array : %@",sortedByDates);

score 2 · Answer 2 · edited May 23 '17 at 12:30

2

Like this:

    NSMutableArray *sortedArray = [arr sortedArrayUsingComparator:^NSComparisonResult(NSDictionary *obj1, NSDictionary *obj2) {
        NSDate *d1 = [self stringToDate:obj1[@"postDate"]];
        NSDate *d2 = [self stringToDate:obj2[@"postDate"]];
        return [d1 compare:d2];
    }];

For the "stringToDate" method, however you want to implement that, see another SO answer here: Convert NSString of a date to an NSDate

Edit: As @Droppy has pointed out, it would really be best to parse the string into a NSDate as soon as the data arrives from the server. That prevents expensive repeated conversion in sorting, and is probably all around more useful anyway.

edited May 23 '17 at 12:30

Community

1
1

answered May 27 '15 at 10:41

n13

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I'm sure that will work, but the repeated conversion of string to date will make it expensive. – Droppy May 27 '15 at 10:42
(even more so if you follow the code you linked and create a new `NSDateFormatter` each time). – Droppy May 27 '15 at 10:43
Sure. But it depends on how many records you have whether or not that would cause a problem. If it did, there's numerous ways to cache the conversion. Not doing that for him either ;) – n13 May 27 '15 at 10:44
... like converting the data to a custom object as soon as it's parsed, for example? – Droppy May 27 '15 at 10:46
Yes that's one option. Spend as much time as you need to make the stringToDate method as fast and as efficient as you need. I wouldn't bother at all if I process, say, 10 records at a time. If theres 100, maybe. If there's 1000, sure. – n13 May 27 '15 at 10:47
@Droppy that's a good idea - maybe. It really depends on the problem space which we don't know anything about. I didn't want to go too overboard with this solution. Just to show how to sort an array of dicts. – n13 May 27 '15 at 10:50
Well the OP has already hit one issue by keeping the data in the form it was delivered in (via JSON I guess). People do not seem to appreciate the time saved by creating a custom Model object for their data. Oh well, their loss... – Droppy May 27 '15 at 10:51
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/78886/discussion-between-n13-and-droppy). – n13 May 27 '15 at 10:52

Jasper · Answer 3 · 2015-05-27T10:59:54.710

You will have to create NSDate objects from those NSString's to make the compare work

Create a static NSDateFormatter as they are expensive to create:

NSArray *sortedArray = [array sortedArrayUsingComparator:^NSComparisonResult(NSDictionary *a, NSDictionary *b) {

        static NSDateFormatter *dateFormatter = nil;
        static dispatch_once_t onceToken;
        dispatch_once(&onceToken, ^{
            dateFormatter = [[NSDateFormatter alloc] init];
            [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"]; //Set correct format here
        });

        NSDate *first = [dateFormatter dateFromString:[a objectForKey:@"postDate"]];
        NSDate *second = [dateFormatter dateFromString:[b objectForKey:@"postDate"]];
        return [first compare:second];
    }];

Sorting NSArray which contain array of dictionaries - Sort as per "Date" key

3 Answers3