WordPress: add additional filter options to post type site for each taxonomy which is used for this plugin

filter_posts.php

function filter_posts() {
	global $typenow;

	if( 'podcast' == $typenow ){

		/* push each taxonomy name, which is used in this plugin
		 * into _tax array. filter_posts() uses this array
		 * to know which taxonomy is used and display filter options
		 * for that
		 */
		foreach ( $_tax as $tax_slug ) {
			$tax_obj = get_taxonomy( $tax_slug );
			$tax_name = $tax_obj->labels->name;
			$terms = get_terms($tax_slug);

			echo "<select name='$tax_slug' id='$tax_slug' class='postform'>";
			echo "<option value=''>Show All $tax_name</option>";

			foreach ( $terms as $term ) {
				$selected = '';
				if ( isset( $_GET[$tax_slug] ) ) {
					if ( $_GET[$tax_slug] == $term->slug )
						$selected = ' selected="selected"';
				}

				echo '<option value='. $term->slug, $selected,'>' . $term->name .' (' . $term->count .')</option>';
			}

			echo "</select>";
		}
	}
}

// add additional filter options to podcast site
add_action( 'restrict_manage_posts', 'filter_posts' );