<?php

     $a=[

         'a'=>['d'=>['aa'=>1,'bb'=>2,'cc'=>3]],

         'b'=>['f'=>['dd'=>4,'ee'=>5,'ff'=>6]],

         'c'=>['g'=>['gg'=>7,'hh'=>8,'ii'=>9]],

         ];

         $b=reduce_arr($a);

         echo '<pre>';

         var_dump($b);

  function reduce_arr ($arr) {

         static $temp = array(); // 声明了一个静态局部变量

         foreach ($arr as $key => $val) {

             if (is_array($val)) {

                 reduce_arr($val);

             } else {

                 $temp[$key] = $val;

             }

         }

         return $temp;

 }

  ?>