php 多維數組簡化（遞歸）

<?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(); // 聲明了一個靜態局部變量

        foreach ($arr as $key => $val) {
            if (is_array($val)) {
                reduce_arr($val);
            } else {
                $temp[$key] = $val;
            }
        }
        return $temp;
}
 ?>