Sort carousel using $args['orderby']

Hello friends,

I need your help with this: I want to sort my carousel of popular coupons as you can see here (the second one) sorting it from comment_count to gdsr_sort with thumbs (using old plugin GD Star rating).

Hoping someone can guide me. I’m a beginner on php. Regards.

Here’s the code who calls the popular coupons carousel to the homepage:

<div class="row collapse">
        <div class="column">
            <div class="items-carousel flexslider">
                <ul class="rr slides">
                    <?php
                    $args = array();
                    $args['posts_per_page'] = 20;
                    $args['post_type'] = 'coupons';
                    $args['orderby'] = 'comment_count';
                    $args['order'] = 'DESC';
                    $query = new WP_Query($args);
                    while($query->have_posts() ) : $query->the_post();
                        $discount = get_post_meta($post->ID, '_single_discount', true);
                        $date = get_post_meta($post->ID, '_single_date', true);
                        $code = get_post_meta($post->ID, '_single_code', true);
                        $url = get_post_meta($post->ID, '_single_url', true);
                        $thumbs = array();
                        $categories = get_the_category();
                        $thumb = wp_get_attachment_url( get_post_thumbnail_id($post->ID) );
                        if($categories) {
                            foreach($categories as $category) {
                                $image = get_option('taxonomy_' . $category->term_id);
                                if($image) {
                                     if($thumb == '') {
                                        $thumb = $image['custom_term_meta'];
                                    }
                                    $category_id = $category->term_id;
                                }
                            }
                        }
                        $daysleft = round( ($date-time()) / 24 / 60 / 60);
                        ?>

And here is the code of functions.php who defines the ‘gdsr_sort’ sorting of posts.

//modify-ing the custom query on category pages

add_action( 'parse_query','changept' );
function changept() {
	if( (is_category() || is_author() ) && !is_admin() ) {
		set_query_var( 'post_type', array( 'post', 'coupons' ) );
	}
	if( (is_category() || is_search() || is_author() || is_tag() ) && !is_admin() ) {
		if(isset($_GET['sort']) && $_GET['sort'] == 'popular') {
          	set_query_var('orderby', 'comment_count');
          	set_query_var('order', 'desc');
        }
        elseif(isset($_GET['sort']) && $_GET['sort'] == 'thumbs') {
            set_query_var('meta_query', array(
                array(
                     	'key' => '_single_date',
                     	'value' =>  strtotime("now"),
                     	'compare' => '>=',
                     	'type' => 'UNSIGNED'
                 	)
            ) );
            set_query_var('gdsr_sort', 'thumbs');
            set_query_var('sort_order', 'desc');
        }