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Question

NSArray of Dates sort

Answer 1

+7 A:

You can use sortedArrayUsingFunction:

Here's some example code.

NSInteger dateSort(id s1, id s2, void *context)
{
    NSDateFormatter* format = (NSDateFormatter*)context;
    NSDate* d1 = [format dateFromString:s1];
    NSDate* d2 = [format dateFromString:s2];

    return [d1 compare:d2];
}

...

-(void)someObjectiveCMethod
{
    NSDateFormatter* format = [[[NSDateFormatter alloc] init] autorelease];

    // Find theses format codes here:
    // http://unicode.org/reports/tr35/tr35-6.html#Date_Format_Patterns
    //
    [format setDateFormat:@"EEEE, MMMM dd, yyyy"];

    NSArray* myArray = getMyArray();
    NSArray* sortedArray = [myArray sortedArrayUsingFunction:dateSort context:format];
}

There are a number of these sorts of sort methods in NSArray. It's worth looking at those to familiarize yourself with them.

nall 2009-10-23 14:39:44

Hmmm...this didn't actually sort the list. Will dig with it.

Chris Van Buskirk 2009-10-23 15:30:58

For efficiency's sake, I'd argue for creating the NSDateFormatter in someObjectiveCMethod, and passing it as the context param. Or, at very least, not using autorelease in dateSort.

Sixten Otto 2009-10-23 15:35:24

I fixed the date format. Sorry about that (needed coffee).

nall 2009-10-23 15:46:21

I also changed to pass the formatter via context. I was just trying to be explicit about things, but Sixten is correct. You wouldn't have it there in real code.

nall 2009-10-23 15:48:36

Perfect! Thanks for the help!

Chris Van Buskirk 2009-10-23 15:55:44

Answer 2

+3 A:

NSArray * unsortedDates = ...;
NSArray * sortedDates = [unsortedDates sortedArrayUsingSelector:@selector(compare:)];

Dave DeLong 2009-10-23 14:43:40

Oh, I was under the impression the array had NSStrings, not NSDates. If it has NSDates, Dave's answer is the right one (less code is good).

nall 2009-10-23 14:45:39

Oh hey, I didn't even think they might be strings. I just assumed that an array of date-looking objects would be dates, because it'd be pretty crazy to store dates any other way.

Dave DeLong 2009-10-23 14:57:52

Yes, sorry, they are strings not nsdates.

Chris Van Buskirk 2009-10-23 15:19:14

I'd edit the title and/or content to make that more apparent. :)

Wevah 2009-10-23 20:55:24

I would suggest making them dates. It's good to keep your date-parsing code and your date-sorting code (separate tasks) in separate places.

Peter Hosey 2009-10-24 01:30:29

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