[WP][WooCommerce] Add featured products filter

wp_wc_filter_by_featured_product.php

<?php
// Add a filter to show featured products, in admin panel for WooCommerce
function woocommerce_filter_products_by_featured_status() {

     global $typenow, $wp_query;

    if ($typenow=='product') :


        // Featured/ Not Featured
        $output .= "<select name='featured_status' id='dropdown_featured_status'>";
        $output .= '<option value="">'.__( 'Show All Featured Statuses', 'woocommerce' ).'</option>';

        $output .="<option value='featured' ";
        if ( isset( $_GET['featured_status'] ) ) $output .= selected('featured', $_GET['featured_status'], false);
        $output .=">".__( 'Featured', 'woocommerce' )."</option>";

        $output .="<option value='normal' ";
        if ( isset( $_GET['featured_status'] ) ) $output .= selected('normal', $_GET['featured_status'], false);
        $output .=">".__( 'Not Featured', 'woocommerce' )."</option>";

        $output .="</select>";

        echo $output;
    endif;
}
add_action('restrict_manage_posts', 'woocommerce_filter_products_by_featured_status');

function woocommerce_featured_products_admin_filter_query( $query ) {
    global $typenow;

    if ( $typenow == 'product' ) {

        // Subtypes
        if ( ! empty( $_GET['featured_status'] ) ) {
            if ( $_GET['featured_status'] == 'featured' ) {
                $query->query_vars['tax_query'][] = array(
                    'taxonomy' => 'product_visibility',
                    'field'    => 'slug',
                    'terms'    => 'featured',
                );
            } elseif ( $_GET['featured_status'] == 'normal' ) {
                $query->query_vars['tax_query'][] = array(
                    'taxonomy' => 'product_visibility',
                    'field'    => 'slug',
                    'terms'    => 'featured',
                    'operator' => 'NOT IN',
                );
            }
        }

    }

}
add_filter( 'parse_query', 'woocommerce_featured_products_admin_filter_query');

?>