Modified mp_related_products function

<?php

if (!function_exists('mp_related_products')) :
/**
 * Displays related products for the passed product id
 *
 * @param int $product_id.
 * @param bool $in_same_category Optional, whether to limit related to the same category.
 * @param bool $echo. Optional, whether to echo or return the results
 * @param int $limit. Optional The number of products we want to retrieve.
 * @param bool $simple_list Optional, whether to show the related products based on the "list_view" setting or as a simple unordered list
 * @param bool $in_same_tags Optional, whether to limit related to same tags
 */
function mp_related_products() {
    global $mp, $post;

    $output = '';
    $categories = $tag_list = array();

    if( $mp->get_setting('related_products->show') == 0)
        return '';

    $defaults = array_merge($mp->defaults['related_products'], array(
        'simple_list' => $mp->get_setting('related_products->simple_list'),
        'relate_by' => $mp->get_setting('related_products->relate_by'),
        'limit' => $mp->get_setting('related_products->show_limit'),
    ));

    $args = $mp->parse_args(func_get_args(), $defaults);

    if( !is_null($args['product_id']) ) {
        $args['product_id'] = ( isset($post) && $post->post_type == 'product' ) ? $post->ID : false;
        $product_details = get_post($args['product_id']);
    }else{
        $product_details = get_post($args['product_id']);
        $args['product_id'] = ( $product_details->post_type == 'product' ) ? $post->ID : false;
    }

    if( is_null($product_details) )
        return '';

    //setup the default args
    $query_args = array(
        'orderby' => 'title',
        'order'   => 'DESC',
        'post_type'      => 'product',
        'posts_per_page' => intval($args['limit']),
        'post__not_in'   => array($args['product_id']),
        'tax_query'      => array(), //we'll add these later
    );

    //get the tags for this product
    if ( 'both' == $args['relate_by'] || 'tags' == $args['relate_by'] ) {
        $tags = get_the_terms( $args['product_id'], 'product_tag');

        if ( is_array($tags) ) {
            foreach($tags as $tag) {
                $tag_list[] = $tag->term_id;
            }

            //add the tag taxonomy query
            $query_args['tax_query'][] = array(
                    'taxonomy' => 'product_tag',
                    'field' => 'id',
                    'terms' => $tag_list,
                    'operator' => 'IN'
            );
        }
    }

    //are we limiting to only the assigned categories
    if( 'both' == $args['relate_by'] || 'category' == $args['relate_by'] ) {
        $product_cats = get_the_terms( $args['product_id'], 'product_category' );

        if( is_array($product_cats) ) {
            foreach($product_cats as $cat) {
                $categories[] = $cat->term_id;
            }

            $query_args['tax_query'][] = array(
                    'taxonomy' => 'product_category',
                    'field' => 'id',
                    'terms' => $categories,
                    'operator' => 'IN'
            );
        }
    }

    //we only want to run the query if we have categories or tags to look for.
    if ( count($tag_list) > 0 || count($categories) > 0 ) {
        //make the query
        $related_query = new WP_Query($query_args);

        //how are we formatting the output
        if( $args['simple_list'] ) {

            $output = '<div id="mp_related_products">';
            $output .= '<div class="mp_related_products_title"><h4>' . apply_filters( 'mp_related_products_title', __('Related Products','mp') ) . '</h4></div>';
            if( $related_query->post_count ) {
                $list = '<ul class="mp_related_products_list">%s</ul>';
                $items = '';
                foreach($related_query->posts as $product) {
                    $items .= '<li class="mp_related_products_list_item"><a href="'.get_permalink($product->ID).'">'.$product->post_title.'</a></li>';
                }
                $output .= sprintf($list, $items);
            }else{
                $output .= '<div class="mp_related_products_title"><h4>'. apply_filters( 'mp_related_products_title_none', __('No Related Products','mp') ) . '</h4></div>';
            }

            $output .= '</div>';
        } else {
            //we'll use the $mp settings and functions
            $layout_type = $mp->get_setting('list_view');
            $output = '<div id="mp_related_products" class="mp_' . $layout_type . '">';
            //do we have posts?
            if( $related_query->post_count ) {
                $output .= '<div class="mp_related_products_title"><h4>' . apply_filters( 'mp_related_products_title', __('Related Products','mp') ) . '</h4></div>';
                $output .= $layout_type == 'grid' ? _mp_products_html_grid($related_query) : _mp_products_html_list($related_query);
            }else{
                $output .= '<div class="mp_related_products_title"><h4>'. apply_filters( 'mp_related_products_title_none', __('No Related Products','mp') ) . '</h4></div>';
            }

            $output .= '</div>';
        }
    }

    $output = apply_filters('mp_related_products', $output, $args);

    //how are we sending back the data
    if($args['echo']) {
        echo $output;
    }else{
        return $output;
    }
}
endif;