CUSTOM ADMIN FILTER: Add taxonomy filter to wp-admin posts listing

admin.php

/**************************************************************************************
 *  CUSTOM ADMIN FILTER
 *  Add taxonomy filter to wp-admin posts listing
 **************************************************************************************/

add_action( 'restrict_manage_posts', 'my_restrict_manage_posts' );
function my_restrict_manage_posts() {

    global $typenow;

    wp_dropdown_categories( array(
        'taxonomy' => 'ciudad',
        'hide_empty' => false,
        'hierarchical' => 1,
        'show_option_all' => __('Filtrar por guía', THEME_DOMAIN),
        'walker' => new Walker_TaxonomyDropdown,
        'orderby' => 'name',
        'id' => 'select-location',
        'name' => 'ciudad'
    ));

    if ( $typenow === 'negocio') {
        wp_dropdown_categories( array(
            'taxonomy' => 'categoria',
            'hide_empty' => false,
            'hierarchical' => 1,
            'show_option_all' => __('Tipo de Negocio', THEME_DOMAIN),
            'walker' => new Walker_TaxonomyDropdown,
            'orderby' => 'name',
            'id' => 'select-location',
            'name' => 'categoria'
        ));

    }

}

walker.php

/**
 * Create HTML dropdown list of Categories.
 *
 * @package WordPress
 * @since 2.1.0
 * @uses Walker
 */
class Walker_TaxonomyDropdown extends Walker_CategoryDropdown {
    /**
     * @see Walker::$tree_type
     * @since 2.1.0
     * @var string
     */
    var $tree_type = 'category';

    /**
     * @see Walker::$db_fields
     * @since 2.1.0
     * @todo Decouple this
     * @var array
     */
    var $db_fields = array ('parent' => 'parent', 'id' => 'term_id');

    /**
     * Start the element output.
     *
     * @see Walker::start_el()
     * @since 2.1.0
     *
     * @param string $output   Passed by reference. Used to append additional content.
     * @param object $category Category data object.
     * @param int    $depth    Depth of category. Used for padding.
     * @param array  $args     Uses 'selected' and 'show_count' keys, if they exist. @see wp_dropdown_categories()
     */
    function start_el( &$output, $category, $depth = 0, $args = array(), $id = 0 ) {
        $pad = str_repeat(' ', $depth * 3);

        /** This filter is documented in wp-includes/category-template.php */
        $cat_name = apply_filters( 'list_cats', $category->name, $category );
        //$cat_permalink = get_term_link( $category );
        $cat_permalink = add_query_arg($category->taxonomy, $category->slug);

        $output .= "\t<option data-permalink=\"".$cat_permalink."\" class=\"level-$depth\" value=\"".$category->slug."\"";
        if ( $category->term_id == $args['selected'] )
            $output .= ' selected="selected"';
        $output .= '>';
        $output .= $pad.$cat_name;
        if ( $args['show_count'] )
            $output .= '&nbsp;&nbsp;('. number_format_i18n( $category->count ) .')';
        $output .= "</option>\n";
    }
}