How to do a natural sort on an NSArray?

Question

I've got an array of objects, and I need them sorted by their "title" key. It's currently working, though it's using an ASCII sort instead of a natural sort. The titles are filenames, so they look like this:

file1
file2
file3
...
file10
file11
file12

I'm getting, as you would expect:

file1
file10
file11
file12
file2
file3
...

Does anyone know if there is a way built-in to the NSArray sorting functionality to get this natural sorting as opposed to the alphabetical sort? I found some generic algorithms, but I was hoping for something built-in...

Answer 1

NSStrings can be compared using the NSNumericSearch compare option.

One version:

NSInteger sort(Obj* a, Obj* b, void*) {
    return [[a title] compare:[b title] options:NSNumericSearch];
}

result = [array sortedArrayUsingFunction:&sort context:nil];

Or a bit more generic:

NSInteger sort(id a, id b, void* p) {
    return [[a valueForKey:(NSString*)p] 
            compare:[b valueForKey:(NSString*)p]
            options:NSNumericSearch];
}

result = [array sortedArrayUsingFunction:&sort context:@"title"]

Or using blocks:

result = [array sortedArrayUsingComparator:^(Obj* a, Obj* b) { 
    return [[a title] compare:[b title] options:NSNumericSearch]; 
}];

Answer 2

Those attempting to replicate the Finder's sorting behavior on Mac OS X 10.6 and later (not the iPhone OS, currently) can use localizedStandardCompare: as the comparator selector.

Those with the same goal on earlier versions of Mac OS X and/or on the iPhone OS should use the solution described in the String Programming Guide.

There is a third solution, but it is harder, potentially slower, and not available on the iPhone OS.