Sorting an array of Objective-c objects

Question

So I have a custom class Foo that has a number of members:

@interface Foo : NSObject {
    NSString *title;
    BOOL     taken;
    NSDate   *dateCreated;
}

And in another class I have an NSMutableArray containing a list of these objects. I would very much like to sort this array based on the dateCreated property; I understand I could write my own sorter for this (iterate the array and rearrange based on the date) but I was wondering if there was a proper Objective-C way of achieving this?

Some sort of sorting mechanism where I can provide the member variable to sort by would be great.

In C++ I used to overload the < = > operators and this allowed me to sort by object, but I have a funny feeling Objective-C might offer a nicer alternative?

Many thanks

Have a look at this question: stackoverflow.com/questions/805547/… — schaechtele
– schaechtele, Commented May 6, 2010 at 11:21

Pawel · Accepted Answer · 2010-05-09 09:22:18Z

15

That's quite simple to do.

First, in your Foo object, create a method

- (NSComparisonResult) compareWithAnotherFoo:(Foo*) anotherFoo;

Which will return

[[self dateCreated] compare:[anotherFoo dateCreated]];

In the end, call on the array

[yourArray sortUsingSelector:@selector(compareWithAnotherFoo:)];

Hope this helps, Paul

edited May 9, 2010 at 9:22

answered May 6, 2010 at 11:19

Pawel

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4 Comments

davbryn Over a year ago

Nice concise solution, though I had to change compareWithDate to compare.

Groot Over a year ago

@Pawel This works fine but with characters as å ä ö the sorting is a bit off. (å and ä appears after a and ö after o). You don't happen to know how to solve this?

Pawel Over a year ago

@Filip the order you have described seems to be fine as å and ä are just versions of letter a with diacritic marks added. What exactly is the behaviour you would expect?

Groot Over a year ago

@Pawel Oh, sorry was in my own little swedish bubble, å ä ö appears after xyz in the swedish alphabet as ..xyzåäö. I managed to solve this using the following comparison method: - (NSComparisonResult) compareSongWithSong:(Song *)otherSong { return [[self title] compare:[otherSong title] options:NSCaseInsensitiveSearch range:NSMakeRange(0, self.title.length) locale:[[NSLocale alloc] initWithLocaleIdentifier:@"sv_SE"]]; } Hope it helps someone!

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