Online PHP editor | output for XdO1X

<?php $myarray = [ [0, 70, 19, 0], [0, 24, 14], // note missing 4th element [0, 15, 11, 0], [0, 15, 27, 0] ]; for ($i = count($myarray) - 2; $i >= 0; --$i) { // start from 2nd last subarray, and move toward the start $max = max(count($myarray[$i]), count($myarray[$i+1])); // make sure all elements are accounted for for($k = 0; $k < $max; ++$k) { // iterate and perform subtractions / declarations $myarray[$i][$k] = ($myarray[$i][$k] ?? 0) - ($myarray[$i+1][$k] ?? 0); // declare/overwrite new values as encountered } } var_export($myarray);