将数组某键值抽出作为新数组

<?php
$arr=array(array('id'=>'1','name'=>'lily','start'=>'20110101','end'=>'20110103'),
array('id'=>'2','name'=>'may','start'=>'20110101','end'=>'20110105'));


$new=array();
foreach($arr as $a){
$new[].=$a['id'];
}
print_r($new);
?>