php实现多维数组中每个单元值(数字)翻倍的方法

<?php
$arr = array(1,3,'a'=>20,'b'=>array(2,4,6,'c'=>7));
function arr2($arr){
 foreach($arr as $key=>$v){
 if(!is_array($v)){
  $arr[$key] = 2;
 }else{
  $arr[$key] = arr2($arr[$key]);
 }
 }
 return $arr;
}
echo "<pre>";
print_r(arr2($arr));
?>

<?php
$arr = array(1,3,'a'=>20,'b'=>array(2,4,6,'c'=>7));
function t(&$arr){ 
 $arr = 2;
}
echo "<pre>";
array_walk_recursive($arr,'t');
print_r($arr);
?>