Dropdown menus to sort by custom taxonomies

functions.php

function taxonomy_filter_restrict_manage_posts() {
    global $typenow;

    // If you only want this to work for your specific post type,
    // check for that $type here and then return.
    // This function, if unmodified, will add the dropdown for each
    // post type / taxonomy combination.

    $post_types = get_post_types( array( '_builtin' => false ) );

    if ( in_array( $typenow, $post_types ) ) {
    	$filters = get_object_taxonomies( $typenow );

        foreach ( $filters as $tax_slug ) {
            $tax_obj = get_taxonomy( $tax_slug );
            wp_dropdown_categories( array(
                'show_option_all' => __('Show All '.$tax_obj->label ),
                'taxonomy' 	  => $tax_slug,
                'name' 		  => $tax_obj->name,
                'orderby' 	  => 'name',
                'selected' 	  => $_GET[$tax_slug],
                'hierarchical' 	  => $tax_obj->hierarchical,
                'show_count' 	  => false,
                'hide_empty' 	  => true
            ) );
        }
    }
}

add_action( 'restrict_manage_posts', 'taxonomy_filter_restrict_manage_posts' );

function taxonomy_filter_post_type_request( $query ) {
  global $pagenow, $typenow;

  if ( 'edit.php' == $pagenow ) {
    $filters = get_object_taxonomies( $typenow );
    foreach ( $filters as $tax_slug ) {
      $var = &$query->query_vars[$tax_slug];
      if ( isset( $var ) ) {
        $term = get_term_by( 'id', $var, $tax_slug );
        $var = $term->slug;
      }
    }
  }
}

add_filter( 'parse_query', 'taxonomy_filter_post_type_request' );