cocoa - Help sorting an NSArray across two properties (with NSSortDescriptor?)

Question

I'm a bit of a NSSortDescriptor n00b. I think, though, it is the right tool for what I need to do:

I have an NSArray consisting of objects with keys, say, "name" and "time". Instead of verbalizing it, here's an example:

input:

name: time
B: 4
C: 8
B: 5
C: 4
A: 3
C: 2
A: 1
A: 7
B: 6


desired output:

name: time
A: 1 <---
A: 3
A: 7
C: 2 <---
C: 4
C: 8
B: 4 <---
B: 5
B: 6

So the values are sorted by "time" and grouped by "name". A comes first because he had the smallest time value, and all values for A come after one another. Then comes C, he had the second smallest time value out of all his values. I have indicated the values that determine how the names are sorted; within each name group, sorting is by time.

How do I get from input to output NSArray in the most efficient way? (cpu- and memory-wise, not necessarily code-wise.) How would I construct the NSSortDescriptors for this, or use any other method? I don't want to roll my own unless it's the most efficient way.

Answer 1

My solution is:

    NSSortDescriptor *sortDescriptor1 = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];
    NSSortDescriptor *sortDescriptor2 = [[NSSortDescriptor alloc] initWithKey:@"time" ascending:YES];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor1, sortDescriptor2, nil];

You can try it