How To Add Weighted Related Posts

function wcs_related_posts(
        $post_id=1,
        $match_limit=5,
        $exclude_list='',
        $before_item='',
        $after_item=', ',
        $before_content='Related Articles: ',
        $after_content='',
        $none_msg='(no keyword matches)',
        $none_to_cats=1
        )
{
    echo wcs_get_related_posts($post_id, $match_limit, $exclude_list, $before_item,
        $after_item, $before_content, $after_content, $none_msg, $none_to_cats);
}

function wcs_get_related_posts(
        $post_id=1,
        $match_limit=5,
        $exclude_list='',
        $before_item='',
        $after_item=', ',
        $before_content='Related Articles: ',
        $after_content='',
        $none_msg='(no keyword matches)',
        $none_to_cats=1
        )
{
    // reference: http://codex.wordpress.org/Function_Reference/WP_Query
 
    // this function should be called from within the loop; but not mandatory
    // $none_msg is displayed if there are no articles with matched tags (keywords)
    // output list is alphabetical, but weighted toward articles with multiple tag matches
    // plugins offer greater functionality, but this can be part of a single.php file
 
    // $exclude_list should not used in single.php unless you want to permanently
    // exclude certain posts; it's best used outside the loop for a list of related posts
 
    // init
    global $post, $wpdb;
    $backup = $post;
    $posts_list = array();
    $links = array();
    $exc_array = array();
    $output = '';
    $i = 0;
    $link_max = 0;
    $exc_array_size = 0;
    $max_matches_per_tag = -1; // -1 = match ALL articles with each tag
 
    // prep for processing
    $tags = wp_get_post_tags($post_id);
    $tag_count = sizeof($tags);
 
    // begin processing
    if ($tag_count > 0)
    {
        for ($i = 0; $i < $tag_count; $i++)
        {
            $this_query = null;
            $this_tag = $tags[$i]->term_id;
            $args = array
            (
                'tag__in' => array($this_tag),
                'post_type' => 'post',
                'post_status' => 'publish',
                'post__not_in' => array($post_id), // ignore current
                'posts_per_page' => $max_matches_per_tag,
                'ignore_sticky_posts' => 1
            );
            $this_query = new WP_Query($args);
 
            if($this_query->have_posts())
            {
                while ($this_query->have_posts())
                {
                    $this_query->the_post(); // get data for this post
                    $posts_list[] = $post->post_name; // slug
                }
            }
        }
 
        if (sizeof($posts_list) > 0)
        {
            // remove excluded items
            if ($exclude_list != '')
            {
                $exclude_list = preg_replace('/\s+/', '', $exclude_list);
                $exc_array = explode(',', $exclude_list);
                $exc_array_size = sizeof($exc_array);
                // check for page id's instead of slugs (slows the process)
                for ($i = 0; $i < $exc_array_size; $i++)
                {
                    if (is_numeric($exc_array[$i]))
                    {
                        $exc_array[$i] = $wpdb->get_var("SELECT post_name FROM $wpdb->posts WHERE ID = '" . $exc_array[$i] . "' and post_status='publish' LIMIT 1");
                    }
                }
                // now remove them and resquence
                $posts_list = array_diff($posts_list, $exc_array);
                $posts_list = array_values($posts_list);
            }
 
            // sort alphabetically, but give duplicates highest priority
            rsort(&$posts_list, SORT_STRING);
            $posts_list_sorted = array_count_values($posts_list);
            arsort(&$posts_list_sorted, SORT_NUMERIC);
 
            // begin output string
            $output = $before_content;
 
            // now construct the links
            foreach ($posts_list_sorted as $key => $val)
            {
                $post_id = $wpdb->get_var("SELECT ID FROM $wpdb->posts WHERE post_name = '" . $key . "' and post_status='publish' LIMIT 1");
                $permalink = get_permalink($post_id);
                $title = get_the_title($post_id);
                $links[] = '<a href="' . $permalink . '" rel="bookmark">' . $title . '</a>';
            }
 
            // continue output string
            $link_max = sizeof($links);
            if ($link_max > $match_limit) {$link_max = $match_limit;}
            for ($i = 0; $i < $link_max; $i++)
            {
                $output .= $before_item . $links[$i];
                if ($i < $link_max - 1)
                {
                    $output .= $after_item;
                }
                else
                {
                    // omit possible trailing comma
                    $output .= str_replace(',', '', $after_item);
                }
            }
            $output .= $after_content;
        }
        else
        {
            if ($none_to_cats == false)
            {
                $output = $before_content . $none_msg . $after_content;
            }
            else
            {
                $output = $before_content;
                $output .= wcs_get_category_posts_list(
                        $post_id, $match_limit,
                        $before_item, $after_item,
                        $none_msg);
                $output .= $after_content;
            }
        }
    }
    else
    {
        if ($none_to_cats == false)
        {
            $output = $before_content . $none_msg . $after_content;
        }
        else
        {
            $output = $before_content;
            $output .= wcs_get_category_posts_list(
                    $post_id, $match_limit,
                    $before_item, $after_item,
                    $none_msg);
            $output .= $after_content;
        }
    }
 
    // exit
    $post = $backup;
    wp_reset_query();
    return $output;
}
    /**********************************************************************
     Copyright © 2011 Gizmo Digital Fusion (http://wpCodeSnippets.info)
     you can redistribute and/or modify this code under the terms of the
     GNU GPL v2: http://www.gnu.org/licenses/gpl-2.0.html
    **********************************************************************/
}

function wcs_get_category_posts_list(
        $post_id=1,
        $match_limit=5,
        $before_item='',
        $after_item=', ',
        $none_msg='(no keyword matches)'
        )
{
    // init
    global $post, $wpdb;
    $backup = $post;
    $output = '';
 
    // get list of categories for this post
    $cat_array = get_the_category($post_id);
    $cat_count = sizeof($cat_array);
    if ($cat_count == 0) {return $none_msg;}
 
    // get first top-level category
    $first_top_cat_id = 0;
    for($i = 0; $i <= $cat_count; $i++)
    {
        if ($cat_array[$i]->parent == 0)
        {
            $first_top_cat_id = $cat_array[$i]->term_id;
            break;
        }
    }
    if ($first_top_cat_id == 0) {return $none_msg;}
 
    // get posts for the first top-level category
    $args = 'cat=' . $first_top_cat_id;
    $args .= '&posts_per_page=' . $match_limit;
    $args .= '&post_status=publish&orderby=post_date&order=DESC';
    $this_query = new WP_Query($args);
 
    // construct list of posts for the first top-level category
    if($this_query->have_posts())
    {
        $counter = 1;
        $this_count = $this_query->post_count;
        while ($this_query->have_posts())
        {
            // construct single item
            $this_query->the_post(); // get data for this post
            if ($post->ID != $post_id) // omit current post
            {
                $output .= $before_item;
                $output .= '<a href="' . get_permalink() . '">';
                $output .= get_the_title() . '</a>';
                if ($counter != $this_count) {$output .= $after_item;}
                // strip a possible final comma in the list
                else {$output .= str_replace(',', '', $after_item);}
            }
            $counter++;
        }
    }
    else
    {
        $output = $none_msg;
    }
 
    // exit
    $post = $backup;
    wp_reset_query();
    return $output;
}