php数组过滤有关问题

php数组过滤问题
假设数组
array(0 => array('catid' => 10 , 'parent' => '1') , 1 => array('catid' => 11 , 'parent' => 1) , array('catid' => 21 , 'parent' => 2) );

我希望只保留 parent 为2的值要怎么做呢？
小弟新人希望大侠帮忙 谢谢！
php

------解决方案--------------------

$a = array(0 => array('catid' => 10 , 'parent' => '1') , 1 => array('catid' => 11 , 'parent' => 1) , array('catid' => 21 , 'parent' => 2) );

$t = array_map(function($v) { return array('parent' => $v['parent']); }, $a);

/*

php 5.2.x 写作

$t = array_map(create_function('$v', 'return array("parent" => $v["parent"]);'), $a);

*/

print_r($t);

Array
(
[0] => Array
(
[parent] => 1
)

[1] => Array
(
[parent] => 1
)

[2] => Array
(
[parent] => 2
)

)

------解决方案--------------------
function intersect2nd($arr1, $arr2, $key)
{
foreach($arr2 as $v) $tmpArr[] = $v[$key];
foreach($arr1 as $k=>$v) if(in_array($v[$key], $tmpArr)) $arr[$k] = $v;
return $arr;
}
$a=array(0 => array('catid' => 10 , 'parent' => '1') , 1 => array('catid' => 11 , 'parent' => 1) , array('catid' => 21 , 'parent' => 2) );
$b=array(array('parent' => 2)); //这个自己编一个类似数组，包含所需key和值就行
$c= intersect2nd($a, $b, 'parent');
var_export($c);

记忆中这是版主唠叨的代码，不敢僭越