Mutlidimensional array not sorting with PHP usort correctly

Question

I can't get this. Why doesn' this work?

    $list = array(array('id' => 123), array('id' => 10), array('id' => 1000));
    $this->OrderListById($list);
    return $list;

    public function OrderListById($list){
        usort($list, function($a, $b) {return $a['id'] - $b['id'];});
    }

This returns

array(
    (int) 0 => array(
        'id' => (int) 123
    ),
    (int) 1 => array(
        'id' => (int) 10
    ),
    (int) 2 => array(
        'id' => (int) 1000
    )
)

And i was hoping something like more ordered :D

array(
    (int) 0 => array(
        'id' => (int) 10
    ),
    (int) 1 => array(
        'id' => (int) 123
    ),
    (int) 2 => array(
        'id' => (int) 1000
    )
)

possible duplicate of [Sort Multi-dimensional Array by Value](http://stackoverflow.com/questions/2699086/sort-multi-dimensional-array-by-value) — Mr. Alien, Jan 13 '14 at 14:52

score 4 · Accepted Answer · answered Jan 13 '14 at 14:53

4

The $list parameter in the OrderListById must be a reference:

public function OrderListById(array &$list)
{
    usort($list, function($a, $b) {
        return $a['id'] - $b['id'];
    });
}

Should work.

As a precaution you could typecast values as you compare them, just in case they are not integers, however, that's something you should check before you sort the array:

return (int) $a['id'] - (int) $b['id'];

answered Jan 13 '14 at 14:53

Andris

5,853
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Ha! It's always something simple, isn't it. Glad to help! – Andris Jan 13 '14 at 14:55

score 4 · Answer 2 · answered Jan 13 '14 at 14:53

4

return $a['id'] - $b['id'];

1000-123 is more than 123-10.

This should be more like the example, where you do a comparison, not subtraction.

function cmp($a, $b)
{
    if ($a == $b) {
        return 0;
    }
    return ($a < $b) ? -1 : 1;
}

In one line that would be:

usort($list, function($a, $b) {return ($a['id'] == $b['id'] ? 0 : (($a['id'] < $b['id']) ? -1 : 1)); });

(not tested, might be a typo, but that's the jist of it)

answered Jan 13 '14 at 14:53

Jessica

7,075
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Working solution as well. Implementation is messier than what I was looking for :D – makallio85 Jan 13 '14 at 14:59

Mark Baker · Answer 3 · 2014-01-13T14:53:57.337

-1

Either pass by Reference:

public function OrderListById(&$list){
    usort($list, function($a, $b) {return $a['id'] - $b['id'];});
}

or return the sorted list

public function OrderListById($list){
    usort($list, function($a, $b) {return $a['id'] - $b['id'];});
    return $list;
}

edited Jan 13 '14 at 14:53

answered Jan 13 '14 at 14:52

Mark Baker

209,507
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Not the downvoter but seems like you hit the answer button in a hurry – Mr. Alien Jan 13 '14 at 14:53
Gee, how many downvotes am I actually going to get for answering hastily (even if the answer is formatted cleanly now) – Mark Baker Jan 13 '14 at 14:55

Mutlidimensional array not sorting with PHP usort correctly

3 Answers3