How can i sort a multi-dimensional array by it's keys in one of it's elements with usort in php?

I know i can easy sort a multi-dimensional array like this:

$array = [["15", "20", "1"], ["16", "25", "2"], ["17", "15", "1"]];

by using compare function and usort in php:

function cmp($a, $b)
{
    return strcmp($a[2], $b[2]);
}
usort($array, "cmp");

But what if i have another array:

$array2 = [["15", "16", "17"], ["20", "25", "15"], ["1", "2", "1"]];

Now, as you can see, things to compare are in last element (array) of the multi-dimensional array. I want to finally have this after sorting:

$array2sorted = [["15", "17", "16"], ["20", "15", "25"], ["1", "1", "2"]];

How can i do it with usort?

>Solution :

You can use array_walk to apply a sorting function to each member of the array. Combined with the PHP 7.4 arrow functions this can look like this:

array_walk($array2, fn (&$subArray) => usort($subArray, /*your logic*/));

EDIT:

Now when I read the question more carefully, this might not work as you requested.

You can use array_multisort instead like this:

$array2 = [["15", "16", "17"], ["20", "25", "15"], ["1", "2", "1"]];

array_multisort($array2[2], ...$array2);

This sorts every item of the array in the way only the last sub-array is sorted.