PHP usort won't sort class

Question

This is a sample of the array of elemnts to sort:

$items = 
    array
      0 => 
        object(stdClass)[8]
          public 'id' => string '110' (length=3)
          public 'brand_id' => string '18' (length=2)
            array
              0 => string ' OT-708' (length=7)
          public 'failed' => null
          public 'diff' => null
      1 => 
        object(stdClass)[9]
          public 'id' => string '161' (length=3)
          public 'brand_id' => string '18' (length=2)

So, let's say I want to sort by brand_id. This is my usort callback function:

function _compare($itemA, $itemB){

    if ($itemA->brand_id == $itemB->brand_id) {

        return 0; 
    }
    else{
        return strcmp($itemA->brand_id, $itemB->brand_id); //just an example...
    }

}

And when I do usort($items, '_compare'); var_dump($items); nothing happens. Any clues on how to troubleshoot this?

--UPDATE--

Ok, I've simplified the problem to this:

function cmp($itemA, $itemB){
    return -1;
}

if (usort($items, "cmp"))
                echo 'I just sorted!';
else echo 'Cant sort!';

It always prints 'Cant sort!'

Angelaangele

brand_name doesn't even exist in those objects. – Hurricane

Are you printing the return of usort or $items? because usort only returns a bool on success / false otherwise. – Tyler

Sorry, guys, I corrected the example. – Angelaangele

I was printing $items. I'll check the compare function return. – Angelaangele

I've updated the question, usort always fails for me. – Angelaangele

@ign it's if (usort($items, "cmp")), NOT if (usort(items, "cmp")), rihgt? – Pubescent

Yes, $items, sorry, I already feel like an idiot. – Angelaangele

@ign you could do var_dump($items); before usort? Does it show anything? Or could you show us more of your code? – Pubescent

OK, I figured it out... My mistake for thinking I had error reporting ON. All this code, including function cmp is inside a class, so I was getting this and didn't realize "( ! ) Warning: usort() expects parameter 2 to be a valid callback, function 'cmp' not found or invalid function name in ..." – Angelaangele

@ign , nice you could now insert your problem solution as an answer and accept it for future readers that could have a similar problem. – Pubescent

Yeah, I will as soon as SO lets me. Thanks for your help, it would have taken me a while more without it. – Angelaangele

Answer 1

Finally, I discovered the source of this error. The problem was that this code was inside a class.

If that's your case, then you should call usort this way:

usort($items, array("MyClass", "compare_method"));

Furthermore, if your Class is in a namespace, you should list the full namespace in usort.

usort($items, array('Full\Namespace\WebPageInformation', 'compare_method'));

Angelaangele

Thanks, got the same problem with uksort. The documentation says uksort will return true or false, and it was returning null. – Cyclohexane

If anyone else is still having issues, try making your compare function static. – Binturong

You can also replace the class name with $this as the first element in the array. This is equiv to $this->compare_method($a, $b) so make sure the function is set to public. Otherwise usort is trying to do MyClass::comapre_method($a, $b) so make sure the function is set to static. – Veta

Answer 2

Also, you can set a static function inside your Class:

static myfunction($a, $b){'yoursort'}

and call it like this:

usort($items, "Class::myfunction");

Weigel

Answer 3

You can also use $this if you use usort in a Class:

usort($my_array, array($this, 'orderByDate'));

Urbanize