关于合并二维数组的有关问题

关于合并二维数组的问题
有一个数组：
Array
(
    [0] => Array
        (
            [a] => Array
                (
                    [id] => 4
                )

        )

    [1] => Array
        (
            [a] => Array
                (
                    [id] => 5
                )

        )

    [2] => Array
        (
            [b] => Array
                (
                    [id] => 4
                )

        )

    [3] => Array
        (
            [b] => Array
                (
                    [id] => 7
                )

        )

)

请问如何合并成
Array(
[0]=>4
[1]=>5
[2]=>4
[3]=>7
)

value都是二维数组id
------解决思路----------------------

$arr = Array<br />(<br />    '0' => Array<br />        (<br />            'a' => Array<br />                (<br />                    'id' => 4<br />                )<br /><br />        ),<br /><br />    '1' => Array<br />        (<br />            'a' => Array<br />                (<br />                    'id' => 5<br />                )<br /><br />        ),<br /><br />    '2' => Array<br />        (<br />            'b' => Array<br />                (<br />                    'id' => 4<br />                )<br /><br />        ),<br /><br />    '3' => Array<br />        (<br />            'b' => Array<br />                (<br />                    'id' => 7<br />                )<br /><br />        )<br /><br />);<br />$new_arr = array();<br />foreach($arr as $vl){<br />    foreach($vl as $v) $new_arr[] = $v['id'];<br />}<br />print_r($new_arr);

------解决思路----------------------

$a = array (<br>  0 => <br>  array (<br>    'a' => <br>    array (<br>      'id' => '4',<br>    ),<br>  ),<br>  1 => <br>  array (<div class="clear">
                 
              
              
        
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