Sort NSArray of custom objects by their NSDate properties

Question

I am attempting to sort an NSArray that is populated with custom objects. Each object has a property startDateTime that is of type NSDate.

The following code results in an array, sortedEventArray, populated but not sorted. Am I going about this the completely wrong way or am I just missing something small?

NSSortDescriptor *dateDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"startDateTime" 
                                                                 ascending:YES];
NSArray *sortDescriptors = [NSArray arrayWithObject:dateDescriptor];
NSArray *sortedEventArray = [nodeEventArray sortedArrayUsingDescriptors:sortDescriptors];

Code seems perfectly fine. Are you sure you have the correct key? — Firoze Lafeer, May 21 '11 at 20:47
@Firoze: Yes, I have triple checked the name. "startDateTime" is the name of the NSDate property on my custom class. — markdorison, May 21 '11 at 22:52
The problem turned out to be elsewhere in my code so I considered closing the question, but due to the helpful nature of the answers below, I am going to leave it here as I think others may find it useful. — markdorison, May 22 '11 at 16:47

score 25 · Accepted Answer · answered May 21 '11 at 22:53

Are you sure that the startDateTime instance variables of the node events are non-nil?

If you don't have one already, you might add a (custom) -description method to your node event objects that does something like this:

- (NSString *)description {
   return [NSString stringWithFormat:@"%@ - %@",
                   [super description], startDateTime]];
}

Then in your sorting code log the array before and after:

NSLog(@"nodeEventArray == %@", nodeEventArray);
NSSortDescriptor *dateDescriptor = [NSSortDescriptor
                                     sortDescriptorWithKey:@"startDateTime" 
                                                 ascending:YES];
NSArray *sortDescriptors = [NSArray arrayWithObject:dateDescriptor];
NSArray *sortedEventArray = [nodeEventArray
         sortedArrayUsingDescriptors:sortDescriptors];
NSLog(@"sortedEventArray == %@", sortedEventArray);

If the startDateTime's are all nil, then the before and after arrays will have the same order (since the sorting operation will equate to sending all the -compare: messages to nil, which basically does nothing).

slottermoser · Answer 2 · 2015-04-21T23:19:48.753

11

Ok, I know this is a little late, but this is how I would do it:

NSArray *sortedEventArray = [events sortedArrayUsingComparator:^NSComparisonResult(Event *event1, Event *event2) {
    return [event1.startDateTime compare:event2.startDateTime];
}];

Obviously, replace Event with the class of your custom object. The advantage of this approach is that you are protected against future refactoring. If you were to refactor and rename the startDateTime property to something else, Xcode probably would not change the string you're passing into the sort descriptor. Suddenly, your sorting code would break/do nothing.

edited Apr 21 '15 at 23:19

answered Oct 04 '12 at 20:24

slottermoser

154
1
5

I agree with you. FYI though, small typo. It's: "sortedArrayUsingComparator:" – Paul Evans Mar 13 '14 at 14:21
@PaulEvans I was using -[NSMutableArray sortUsingComparator:], as I noted in my comment. However, I can change it to return a new sorted array in line with OP's example. Thanks :) – slottermoser Apr 21 '15 at 23:17

score 11 · Answer 3 · answered May 21 '11 at 17:54

11

Did you try by specifying the NSDate comparator?

Eg:

NSSortDescriptor *dateDescriptor = [NSSortDescriptor
   sortDescriptorWithKey:@"startDateTime"
   ascending:YES
   selector:@selector(compare:)];

This should enforce the usage of the correct comparator of the NSDate class.

answered May 21 '11 at 17:54

Jack

131,802
30
241
343

1

This change did not seem to affect my results. – markdorison May 21 '11 at 18:02

score 0 · Answer 4 · edited Mar 17 '15 at 09:12

0

You can achieve this like this,

NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"date" ascending:FALSE];

[self.Array sortUsingDescriptors:[NSArray arrayWithObject:sortDescriptor]];

edited Mar 17 '15 at 09:12

Hemang

26,840
19
119
186

answered Jul 22 '13 at 11:14

Martin Jacob

356
1
7
16

score 0 · Answer 5 · edited Mar 17 '15 at 09:09

0

You can achieve like this,

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

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

edited Mar 17 '15 at 09:09

Hemang

26,840
19
119
186

answered Jan 01 '14 at 07:09

Darshit Shah

2,366
26
33

Sort NSArray of custom objects by their NSDate properties

5 Answers5

Linked

Related