How to sort numbers in NSArray?

Question

I can't piece together how to do this.

I fetch my array from a plist, this array is full of numbers (as set in the plist). Now al I need to do is sort them so they are descending, but I can't work it out.

score 43 · Accepted Answer · answered Jun 24 '12 at 16:53

43

Try this code?

 NSArray *array = /* loaded from file */;
 array = [array sortedArrayUsingSelector: @selector(compare:)];

answered Jun 24 '12 at 16:53

Alexsander Akers

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But what would the contents of the selector method be? This is what gets me. – Josh Kahane Jun 24 '12 at 16:57
2

The `-compare:` method is defined for `NSNumber` instances: https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSNumber_Class/Reference/Reference.html#//apple_ref/occ/instm/NSNumber/compare: – Alexsander Akers Jun 24 '12 at 16:59
Thats the one I meant. Perhaps I misunderstanding the docs, but I have tried with and without the compare method and it always crashing the app saying unrecognised selector. – Josh Kahane Jun 24 '12 at 17:07
That's weird. Something must be up with your array then. – Alexsander Akers Jun 24 '12 at 17:09
Hmm, its literally an arrays which looks like this: 1, 54, 23, 11, 8, 67. I'll look further into it. – Josh Kahane Jun 24 '12 at 17:10
1

It seems that (from your comment on the other answer) that you've populated your .plist with numbers *as strings* and not *as numbers*. – Alexsander Akers Jun 24 '12 at 17:10
Am I the only one who finds this stupidly complicated? There's seriously no method for `NSArray` called `sortedArray` which calls exactly this? I love extensions and all, but why do I (and everyone else) have to write such basic stuff that Apple should have had in the standard libraries all along? Although Obj-C is a flawed language and Swift can't come quickly enough, it seems to me a bigger problem is the lousy libraries. I hope Swift's libraries don't leave me having to write out this basic stuff myself. – ArtOfWarfare Jul 09 '14 at 01:32
@ArtOfWarfare: Since Arrays can hold any type of object, including entire subarrays and dictionaries, it's impossible to have a generic sorting routine that automatically knows how to sort your objects. Let's say you have an array of UIViewControllers. How should they be sorted? – Owen Hartnett Aug 09 '16 at 12:17
@OwenHartnett - It should always use `compare:`. If the class you've inserted into your `NSArray` doesn't implement that method, then you shouldn't be using the `sortedArray` method. You'll have to fall back to the more flexible `sortedArrayUsingSelector:` method. – ArtOfWarfare Aug 09 '16 at 13:25
You can't always use compare: . In objective C, arrays can hold mixed types: You might have a string, and NSNumber, a UIViewController and a NSDate all in the same array, yet there may be logical reason where a sort is appropriate. Having a generic compare: as a default method could generate unattainable expectations and be very difficult to debug without checking the types of the array items. – Owen Hartnett Aug 09 '16 at 18:10

score 16 · Answer 2 · edited May 23 '17 at 12:18

16

The following will sort the numbers in ascending order and then reverse the result to give the numbers in descending order:

NSArray *sorted = [[[array sortedArrayUsingSelector:@selector(compare:)] reverseObjectEnumerator] allObjects];

This previous question has some other alternatives: Sort an NSArray in Descending Order

edited May 23 '17 at 12:18

Community

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answered Jun 24 '12 at 17:07

mttrb

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Im getting a crash with `-[__NSCFString sortedArrayUsingSelector:]: unrecognized selector sent to instance`. – Josh Kahane Jun 24 '12 at 17:09
Are you sure you calling `sortedArrayUsingSelector:` on an `NSArray`? You appear to be calling `sortedArrayUsingSelector:` on an `NSString`. You should probably check the data structure that is being loaded from the Plist. – mttrb Jun 24 '12 at 17:11
@Josh Kahane, if so, you are most likely having issues with memory management, because your `array` pointer points to `NSString` object. Forgot to retain / too much [auto]releases? – ivanzoid Jun 24 '12 at 17:13
This answer fully answer's the question, as it sorts the array *descending*. – adamjansch Nov 11 '19 at 10:35

score 13 · Answer 3 · answered Mar 04 '15 at 17:19

Here is one of many methods using comparison block. This code snippet is handy for any array with numbers that you want to sort. For Ascending order:

AscendingArray = [UnsortArray sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
    if ([obj1 integerValue] > [obj2 integerValue]) {
      return (NSComparisonResult)NSOrderedDescending;
    }

    if ([obj1 integerValue] < [obj2 integerValue]) {
      return (NSComparisonResult)NSOrderedAscending;
    }
    return (NSComparisonResult)NSOrderedSame;
  }];

For Descending order:

DescendingArray = [UnsortArray sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
    if ([obj1 integerValue] > [obj2 integerValue]) {
      return (NSComparisonResult)NSOrderedAscending;
    }

    if ([obj1 integerValue] < [obj2 integerValue]) {
      return (NSComparisonResult)NSOrderedDescending;
    }
    return (NSComparisonResult)NSOrderedSame;
  }];

I've used this method because even if some of my data are numbers, I've stored everything as string. This method can compare numbers that are stored as strings, contrary to compare: method — AnthoPak, Mar 21 '18 at 09:06

score 5 · Answer 4 · edited Jan 26 '15 at 17:06

It work for me:

NSSortDescriptor *sortIdClient = 
[NSSortDescriptor sortDescriptorWithKey:@"campaignValue"
                              ascending:NO
                             comparator: ^(id obj1, id obj2){

    return [obj1 compare:obj2 options:NSNumericSearch];

 }];

NSArray *sortDescriptors = @[sortIdClient];

NSArray *arrTemp = [self.allCampaignsList sortedArrayUsingDescriptors:sortDescriptors];

score 0 · Answer 5 · edited Aug 09 '16 at 13:00

0

This Will solve the problem:

 NSArray *array = /* loaded from file */;
 array = [array sortedArrayUsingSelector: @selector(compare:)];

edited Aug 09 '16 at 13:00

Gustavo Morales

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answered Aug 09 '16 at 12:12

Jasim

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please remove extra indentation which makes text be shown as code – YakovL Aug 09 '16 at 12:33

How to sort numbers in NSArray?

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