how to sort an NSArray of nested NSArrays by array count?

Question

I have an NSArray that contains nested NSArrays. Im looking for a way to sort the parent array according to the object count of the nested arrays in ascending order. so if [array1 count] is 4, [array2 count] is 2 and [array3 count] is 9, i would get : array2, array1, array3...

user557219 · Accepted Answer · 2011-04-30 00:13:34Z

9

There are a few solutions, one of which is:

NSSortDescriptor *sd = [NSSortDescriptor sortDescriptorWithKey:@"@count"
                                                     ascending:YES];
NSArray *sds = [NSArray arrayWithObject:sd];
NSArray *sortedArray = [array sortedArrayUsingDescriptors:sds];

answered Apr 30, 2011 at 0:13

user557219

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4 Comments

user557219 Over a year ago

@Sam Indeed, and you can always use the @count collection operator for KVC compliant collections.

Sam Over a year ago

Ah, my apologies. I wasn't aware of that / misread your code. Very cool!

KDaker Over a year ago

works great!.. i tried it earlier before asking the question but i was using @"count" as key and it was crashing... whats the secret with @"@count"???

user557219 Over a year ago

@KDaker NSArray doesn’t have a KVC compliant key called count. There is an instance method called -count but it isn’t a key in the KVC sense. That said, in Cocoa collections you can use special key paths called collection operators, and @count is one of them.

justin · Accepted Answer · 2011-04-30 00:27:12Z

1

static NSInteger MONSortObjectsAscendingByCount(id lhs, id rhs, void* ignored) {
/* error checking omitted */
    const NSUInteger lhsCount = [lhs count];
    const NSUInteger rhsCount = [rhs count];

    if (lhsCount < rhsCount) {
        return NSOrderedAscending;
    }
    else if (lhsCount > rhsCount) {
        return NSOrderedDescending;
    }
    else {
        return NSOrderedSame;
    }
}

/* use if mutable, and you wnat it sorted in place */
- (void)sortUsingFunction:(NSInteger (*)(id, id, void *))compare context:(void *)context;

/* else use */
- (NSArray *)sortedArrayUsingFunction:(NSInteger (*)(id, id, void *))compare context:(void *)context;

edited Apr 30, 2011 at 0:27

answered Apr 30, 2011 at 0:07

justin

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2 Comments

user557219 Over a year ago

A function whose name doesn’t start with MON? Who are you and what have you done to Justin?

justin Over a year ago

ugggghhhhhhhhhh!!!!!!! =p Justin has a headache today, and the build was finished. thanks for pointing that out -- i've fixed it now =)

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