objective-c custom sorting - sorting

Question

So, having struggled with this for too long, without much documentation to go on, I thought I'd share my experience for those few who are even noobier than me.
There probably are much cleaner ways of achieving what I did, so please feel free to suggest improvements.
Here's what I wanted to do:
I have an NSArrayController which manages NSManagedObjects (say Thing). These objects have a name property which is of type NSString.
I wanted to sort the array of the array controller using the name of the managed objects. The common way to go about sorting a mutable array of strings should be something like:
[myMutableArrayOfStrings sortUsingSelector:#selector(caseInsensitiveCompare:)];
or:
NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:#"name" ascending:YES selector:#selector(caseInsensitiveCompare:)];
NSArray *descriptorArray = [NSArray arrayWithObject:sortDescriptor];
[myArrayController setSortDescriptors:descriptorArray];
However, if the names happened to be numbers, caseInsensitiveCompare: would sort 11 before 8 (for instance).
Also, I wanted a name of a11b to be sorted AFTER a8b, meaning that I needed to chop the names of the managed objects into groups of digits and non-digit characters, then compare those individually.
What I came up with, was to make a category of NSString.
header file:
#import <Foundation/Foundation.h>
#interface NSString (MyString)
- (NSComparisonResult)myCustomCompare:(NSString *)anotherString;
#end
implementation file:
#import "MyString.h"
#implementation NSString (MyString)
- (NSComparisonResult)myCustomCompare:(NSString *)anotherString {
elaborate chopping up of strings into substrings..
For each of the 2 strings I made an NSMutableArray.
Then I determined if these substrings were NSNumbers, which have their own compare:, or NSStrings (caseInsensitiveCompare:)
Then I return an NSComparisonResult (NSOrderedAscending, NSOrderedSame or NSOrderedDescending)
}
#end
Then, in the implementation file of my Thing ManagedObject, I overrid the
- (NSComparisonResult)compare:(Thing *)anotherThing {
return [self.name myCustomCompare:anotherThing.name];
}
One also needs to import MyString.h in the Thing class.
Now, using
[[myArrayController arrangedObjects] sortUsingSelector:#selector(compare:)];
works like a charm.
Just one thing that's been bugging me. If a Thing's name property would contain decimal numbers, like for instance a1.4b and a1.39b, how would I be able to isolate these from the name? (a1.4b would incorrectly be sorted before a1.39b)
To make things even worse, a user could enter a Thing's name to be 1.3.55 ...