Wordpress Popular Post(No. of Post Views)

function.php

<?php
/* Add this code to function.php file */

/* Post View Increment */
function rtp_popular_post(){
    global $post;
    $count_key = '_rtp_post_view_count';
    if(is_single()){
        $view_count = get_post_meta($post->ID, $count_key, true);
        if($view_count==''){
            $view_count = 0;
            //Delete all custom fields with the specified key from the specified post.
            delete_post_meta($post->ID, $count_key);

            //Add a custom (meta) field (Name/value)to the specified post.
            add_post_meta($post->ID, $count_key, '0');
        }
        else
            $view_count++;
            update_post_meta($post->ID, $count_key, $view_count);
    }
}
add_action('wp','rtp_popular_post'); ?>

sidebar.php

<?php
/* Add this code to display post acc. to view count */
$args = array(
                                    'numberposts'     => 4, //get all posts, or set a number here
                                    'offset'          => 0,
                                    'orderby'         => 'meta_value_num', //this will look at the meta_key you set below
                                    'order'           => 'DESC', //You can order by ASC (ascending) or DESC (descending)
                                    'meta_key'        => '_rtp_post_view_count', //Set the meta key here, NOT the meta value.  WordPress will get the value on its own
                                    'post_type'       => 'post', //got a custom post type? Put it here
                                    'post_status'     => 'publish' );
                    $results = get_posts( $args ); 
                  ?>
                <div id="popular-posts-2" class="widget sidebar-widget widget_recent_entries">
                    <h3 class="widgettitle">Popular Posts</h3>
                        <ul>
                            <?php
                                foreach($results as $post_new){
                                    echo '<li><a title="'.$post_new->post_title .'" href="'.  get_permalink($post_new->ID).'">'.$post_new->post_title.'</a></li>';
                                }
                            ?>
                        </ul>
                </div>