Display Most Popular Posts In the Last 30 Days Without plugi

// Display Your Most Popular Posts In the Last 30 Days Without a Plugin

<ul>
<h2><?php echo('Most Popular Posts');?></h2>
<?php
function filter_where($where = '') {
    //posts in the last 30 days
    $where .= " AND post_date > '" . date('Y-m-d', strtotime('-30 days')) . "'";
    return $where;
}
add_filter('posts_where', 'filter_where');

query_posts('post_type=post&posts_per_page=10&orderby=comment_count&order=DESC');

while (have_posts()): the_post(); ?>

<li><a href="<?php the_permalink(); ?>" title="<?php printf(esc_attr('Permalink to %s'), the_title_attribute('echo=0')); ?>" rel="bookmark"><?php the_title(); ?></a>
</li>

<?php
endwhile;
wp_reset_query();
?>
</ul>