objective-C, sort an array of strings containing numbers

Question

Lets suppose I have an array like this

NSArray* arr = @[@"1",@"4",@"2",@"8",@"11",@"10",@"14",@"9"]; //note: strings containing numbers

and I want to sort them like this: [1,2,4,8,9,10,11,14]

but if I use

[arr sortedArrayUsingSelector:@selector(localizedCaseInsensitiveCompare:)];

I get [1,10,11,14,2,4,8,9]... and if I use:

   NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"length" ascending:YES];
   NSArray *sortDescriptors = @[sortDescriptor];
   [arr sortedArrayUsingDescriptors:sortDescriptors];

I get something like this: [1,4,2,8,9,11,10,14]

How can I combine both predicates? or is any other easier way to solve this? note: The output of this array is merely for debug purposes, I dont care if the result turns the array into integers as long as I can print in console with NSLog thanks

actually it would be better a function that returns the numbers missing between the min and the max value... example input: [1,5,4]... output:[2,3] — user2387149, Jun 20 '14 at 16:23

cekisakurek · Accepted Answer · 2017-02-14T08:56:15.540

13

Try using blocks

[arr sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {

    if ([obj1 intValue] == [obj2 intValue])
        return NSOrderedSame;

    else if ([obj1 intValue] < [obj2 intValue])
        return NSOrderedAscending;

    else
        return NSOrderedDescending;

}];

edited Feb 14 '17 at 08:56

answered Jun 20 '14 at 16:20

cekisakurek

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thanks pal, I just had to change the ">" for "<" – user2387149 Jun 20 '14 at 16:41
oh sorry my bad. I updated the answer. – cekisakurek Jun 20 '14 at 18:01
5

The important part of this answer is lost in the minimal explanation. You can sort using blocks or sort descriptors -- it's not *blocks* that make the difference here. The important thing is to use `-intValue` rather than trying to combine `-length` and `-localizedCaseInsensitiveCompare:`. – Caleb Jun 20 '14 at 18:09

score 13 · Answer 2 · answered Jun 20 '14 at 18:12

The problem is that you're trying to use both string comparison and -length to cobble together what you really want, which is numeric comparison. But sort descriptors are applied one at a time, and a second descriptor is only used if the first one orders two items as the same. Using -intValue to order the items lets you use a single sort descriptor that will order the items the way you want.

Do this instead:

NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"intValue" ascending:YES];
[arr sortedArrayUsingDescriptors:@[sortDescriptor]];

objective-C, sort an array of strings containing numbers

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