Sort NSNumber with NSSortDescriptor

Sort NSNumber with NSSortDescriptor

I have a Route as my top level Core Data entity. Then a Route has
Locations. The Locations have a
@property (nonatomic, retain) NSNumber *index;
I need the index because I need to make sure the user's route is in order.
I was wondering how I can best sort on the Locations entity. In my
tableView, I show the name of the Route. Then when the user clicks on the
Route, I show the Locations. I saw NSSet has
sortedArrayUsingDescriptors
but I wasn't aware of how I could sort NSNumber with a sortDescriptor. I
have seen people just use code like
sortedArrayUsingSelector:@selector(compare:) // or something like that
I can write a simple convenience method to iterate through the NSSet and
return the Location objects by their index, but wasn't sure if there was a
better way. Thanks in advance!