Cory Imdieke Cory Imdieke - 5 months ago 20
Objective-C Question

How to do a natural sort on an NSArray?

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

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]; 
}];