Question

I’m using NSSortDescriptor to sort an NSArray of NSDictionary items. Works great, just what I needed… except that I’d like for the dictionary items that have blank values for my sort key to show up at the end of the sorted list. Is there a way to easily accomplish this? Or will I have to create some custom sorting functions? And no, I don’t want to just set it to DESC order… I’d like sorted results to look like A, A, B, B, C, blanks, blank.

Answer 1

Figured this out after seeing another example using a custom comparison. Here is the code I ended up with:

@interface NSString (CustomStatusCompare)
- (NSComparisonResult)customStatusCompare:(NSString*)other;
@end

@implementation NSString (CustomStatusCompare)
- (NSComparisonResult)customStatusCompare:(NSString*)other {
    NSAssert([other isKindOfClass:[NSString class]], @"Must be a NSString");
    if ([self isEqual:other]) {
        return NSOrderedSame;
    }
    else if ([self length] > 0 && [other length] > 0) {
        return [self localizedCaseInsensitiveCompare:other];        
    }
    else if ([self length] > 0 && [other length] == 0) {
        return NSOrderedAscending;
    }
    else {
        return NSOrderedDescending;
    } 
}
@end



NSSortDescriptor *serviceTypeDescriptor =
[[NSSortDescriptor alloc] initWithKey:@"Service"
                             ascending:YES
                             selector:@selector(localizedCaseInsensitiveCompare:)];

NSSortDescriptor *locationDescriptor = 
[[NSSortDescriptor alloc] initWithKey:@"Location"
                             ascending:YES
                             selector:@selector(customStatusCompare:)];  //using custom comparison here!

NSArray *descriptors = [NSArray arrayWithObjects:locationDescriptor, nameDescriptor, nil];        
self.navArray = [self.navArray sortedArrayUsingDescriptors:descriptors];

So the comparer returns NSOrderedSame if both strings are empty… calls the regular comparison function if both strings are non-empty… if only one string is empty, it reverses the normal order of that comparison. Voila!