Easy way to put blank strings at end of sort using NSSortDescriptor?

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.

What do you mean by blank values? No value, empty string, whitespace or `NSNull`? — Costique, Mar 16 '12 at 20:26
I meant empty string. Loading the NSDictionary from a plist, where the value comes from: . — Bryan, Mar 16 '12 at 21:05

score 3 · Accepted Answer · answered Mar 16 '12 at 21:02

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!

Wow, sorry, I somehow totally misread your question and thought you wanted strings with leading blanks first :/ I'll go work on my reading comprehension... — Doug McBride, Mar 19 '12 at 20:08
Note that this won't work within a compile predicate in core data :/ — deepwinter, Apr 11 '18 at 22:49

score 0 · Answer 2 · answered Mar 16 '12 at 20:13

0

Do the Sort using NSNumericSort instead of NSDiacriticInsensitive or NSCaseInsensitive. Since the whitespace is probably 256 in ascii code it will be sent to the back of the list.

answered Mar 16 '12 at 20:13

Panagiotis

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Doug McBride · Answer 3 · 2012-03-19T20:10:17.080

Edit: I misread the question and thought the intent was to put strings with leading spaces first in sort order (which they should anyway).

You want something like this, I think. This is completely untested and doesn't take multiple leading spaces into account. I'm sure there's a more elegant way, but it should get the job done.

NSArray *sortedArray = [array sortedArrayUsingComparator: ^(id obj1, id obj2) {
    NSString *str1 = (NSString *)obj1;
    NSString *str2 = (NSString *)obj2;

    BOOL str1HasSpace = [str1 hasPrefix:@" "];
    BOOL str2HasSpace = [str2 hasPrefix:@" "];

    if (str1HasSpace && !str2HasSpace) {
        return NSOrderedAscending;
    } else if (str2HasSpace && ! str1HasSpace) {
        return NSOrderedDescending;
    } else {
        return [[str1 stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]] compare:[str2 stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]]];
    }
}];

Thanks, I see where you're going here. What I ended up doing was very similar... putting this custom comparison inside its own method in an NSString category (is that the right name?) instead of a block. — Bryan, Mar 16 '12 at 20:55

Easy way to put blank strings at end of sort using NSSortDescriptor?

3 Answers3

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