请大神帮忙 php二维数组重新排序

$a = Array ( Array ('id' => 3, 'username' => 'alex ','parentname'=> 'john'         ,'proname' => 'tttt', 'num'=> 1 ,  'userid' =>6 ,'parentid'=>8 ,   'cpid'=>  0 ,'mobile'=> 15533336666 ,'parentmobile' => 156477765465) );$k = Array ('id', 'username', 'mobile', 'parentname', 'parentmobile', 'proname', 'num', 'userid', 'parentid', 'cpid');foreach($a as $i=>$v) {  extract($v);  $a[$i] = compact($k);}print_r($a);

Array(    [0] => Array        (            [id] => 3            [username] => alex             [mobile] => 15533336666            [parentname] => john            [parentmobile] => 156477765465            [proname] => tttt            [num] => 1            [userid] => 6            [parentid] => 8            [cpid] => 0        ))

<?php$arr = array(    array('id'=>3,'username'=>'alex','parentname'=>'john','proname'=>'tttt','num'=> 1 ,  'userid' =>6 ,'parentid'=>8 ,'cpid'=>  0 ,'mobile'=> 15533336666 ,'parentmobile' => 156477765465),    array('id'=>3,'username'=>'alex','parentname'=>'john','proname'=>'tttt','num'=> 1 ,  'userid' =>6 ,'parentid'=>8 ,'cpid'=>  0 ,'mobile'=> 15533336666 ,'parentmobile' => 156477765465),    array('id'=>3,'username'=>'alex','parentname'=>'john','proname'=>'tttt','num'=> 1 ,  'userid' =>6 ,'parentid'=>8 ,'cpid'=>  0 ,'mobile'=> 15533336666 ,'parentmobile' => 156477765465),);$result = array();$fields = array('id','username','mobile','parentname','parentmobile','proname','num','userid','parentid','cpid');foreach($arr as $k=>$v){    $tmp = array();    foreach($fields as $f){        $tmp[$f] = $v[$f];    }    $result[] = $tmp;}print_r($result);