Adds filter for taxonomies to posts table

wp_add_taxonomy_filter.php

<?php

/**
 * Adds filter for taxonomies to posts table
 *
 * Adapted from:
 * @see http://wordpress.org/support/topic/custom-taxonomy-filter-not-working-in-admin-editphp-31b2?replies=8#post-2400615
 * @see https://wordpress.stackexchange.com/questions/578/adding-a-taxonomy-filter-to-admin-list-for-a-custom-post-type/3215#3215
 *
 * @param array  $taxonomy  Filter to be added
 * @param string $post_type Post type to get filter
 */
function add_taxonomy_filter( $taxonomy, $post_type ) {
	add_action( 'restrict_manage_posts', function() use ( $taxonomy, $post_type ) {
		if ( $GLOBALS['typenow'] == $post_type ) {
			$tax_obj = get_taxonomy( $taxonomy );
			$tax_name = $tax_obj->labels->name;
			$terms = get_terms( $taxonomy );
			$name = ( $taxonomy === 'post_tag' ) ? 'tag' : $taxonomy;
			echo "<select name='$name' id='$taxonomy' class='postform'>";
			echo "<option value=''>All $tax_name</option>";
			if ( !isset( $_GET[$taxonomy] ) ) $_GET[ $taxonomy ] = $taxonomy;
			foreach ( $terms as $term ) {
				echo '<option value='. $term->slug, $_GET[ $name ] == $term->slug ? ' selected="selected"' : '','>' . $term->name .' (' . $term->count .')</option>';
			}
			echo "</select>";
		}
	} );
}