how to resort a array by key 'date'？

Question

Possible Duplicate:
how to sort a multidemensional array by an inner key
How to sort a multidimensional array by a certain key?

I want my array to be sort by date asc, how to do?

<?php
    //how to resort a array by key 'date'？
    $arr=array(
        array(
            'name'=>'a',
            'date'=>'2012-10-21 18:00:00'
        ),
        array(
            'name'=>'x',
            'date'=>'2013-10-21 18:00:00'
        ),
        array(
            'name'=>'d',
            'date'=>'2011-10-21 18:00:00'
        )
    );
?>

Answer 1

function sort_by_date($a, $b) {
  return( $a['date'] < $b['date'] ? -1 : ($a['date'] > $b['date']) ? 1 : 0 );
}

usort($arr, 'sort_by_date');