How to sort a 3-dimensional array by a key in PHP

Question

This is an example of an array that I am trying to sort by the key match_points (descending):

Let the array printed below be called $my_arr.

Array
(
    [0] => Array
        (
            [0] => Array
                (
                    [109] => 92
                    [match_points] => 50
                )

        )

    [1] => Array
        (
            [0] => Array
                (
                    [16] => 12
                    [match_points] => 62
                )

        )

    [2] => Array
        (
            [0] => Array
                (
                    [80] => 51
                    [match_points] => 63
                )

        )

)

I tried this:

$a = usort($my_arr, 
    function (array $a, array $b) { 
        return $a["match_points"] - $b["match_points"]; 
    }
);

But I am getting this warning message:

Undefined index: match_points

This post did not explicitly show how to sort a 3 dimensional array by a specific key, although the answer can be inferred after reading that post.

You have one more array dimension inside each array! Use `var_dump` to see what you're working with. — deceze, Jul 22 '13 at 15:02
does $a[0]["match_points"] and $a[0]["match_points"] help anything? — cocogorilla, Jul 22 '13 at 15:04
@hakre the error message itself wasn't unclear. What was unclear was how to fix it. — lschlessinger, Jul 22 '13 at 15:19
Well I don't understand that. If the error message was clear, why was it unclear to fix it? What specifically was unclear for the fix by that error message? — hakre, Jul 22 '13 at 15:42

score 3 · Accepted Answer · answered Jul 22 '13 at 15:07

The problem is your array is 3 dimensional but your sort is structured for a two dimensional array.

In php 5.3+ you can use usort with a closure

 usort($array, function($a, $b){return $a[0]["match_points"] - $b[0]["match_points"];});

Prior to 5.3 you have define a sorter function.

 function compMatchPoints($a, $b) {
      return $a[0]["match_points"] - $b[0]["match_points"];
 }
 usort($array, "compMatchPoints");

score 1 · Answer 2 · answered Mar 07 '19 at 06:56

Change all the $data variable to your array variable name

 $sortkeys = array();
    foreach ($data as $row) {
        $sortkeys[] = $row[0]['match_points'];
    }

// sort $data according to $sortkeys and use SORT_DESC for descending order

array_multisort($sortKeys,SORT_DESC, $data, SORT_DESC);

echo "<pre>"
print_r($data);
die;

How to sort a 3-dimensional array by a key in PHP

2 Answers2