PHP custom array mapping function which supports key/index

array-mapx.php

<?php
/**
 * PHP default array map function doesn't provide access to array item key
 * So there is no way to map array based on some condition which depends on
 * array item key. And that's why array_mapx is here to help you in that case. 
 * @param  array    $arr           Array that is going to be mapped
 * @param  callable $callback      Callback function to map array $a
 * @param  boolean  $preserve_keys To maintain the old keys
 * @return array                   Mapped array
 */
function array_mapx(array $arr, callable $callback, $preserve_keys = true) {
    $r = [];
    while($k = key($arr)) {
        if ($preserve_keys) {
            $r[$k] = $callback(current($arr), $k);
        } else {
            array_push($r, $callback(current($arr), $k));
        }
        next($arr);
    }
    return $r;
}