Sort NSArray of date strings or objects

If I have an NSMutableArray of objects with a field "beginDate" of type NSDate I am using an NSSortDescriptor as below:

NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"beginDate" ascending:TRUE];
[myMutableArray sortUsingDescriptors:[NSArray arrayWithObject:sortDescriptor]];
[sortDescriptor release];

You may also use something like the following:

//Sort the array of items by  date
    [self.items sortUsingComparator:^NSComparisonResult(id obj1, id obj2){
        return [obj2.date compare:obj1.date];
    }];

But this does assume that the date is stored as a NSDate rather a NString, which should be no problem to make/do. Preferably, I recommend also storing the data in it's raw format. Makes it easier to manipulate in situations like this.

You can use blocks to sort in place:

sortedDatesArray = [[unsortedDatesArray sortedArrayUsingComparator: ^(id a, id b) {
    NSDate *d1 = [NSDate dateWithString: s1];
    NSDate *d2 = [NSDate dateWithString: s2];
    return [d1 compare: d2];
}];

I suggest you convert all your strings to dates before sorting not to do the conversion more times than there are date items. Any sorting algorithm will give you more string to date conversions than the number of items in the array (sometimes substantially more)

a bit more on blocks sorting: http://sokol8.blogspot.com/2011/04/sorting-nsarray-with-blocks.html

Store the dates as NSDate objects in an NS(Mutable)Array, then use -[NSArray sortedArrayUsingSelector: or -[NSMutableArray sortUsingSelector:] and pass @selector(compare:) as the parameter. The -[NSDate compare:] method will order dates in ascending order for you. This is simpler than creating an NSSortDescriptor, and much simpler than writing your own comparison function. (NSDate objects know how to compare themselves to each other at least as efficiently as we could hope to accomplish with custom code.)