PHP: post_class() filter - add custom post classes

post_class_filter.php

<?php

  // Practically verbatim from the WordPress codex
  // http://codex.wordpress.org/Function_Reference/post_class#Add_Classes_By_Filters

  add_filter('post_class','MYTHEME_post_class_cats');

  function MYTHEME_post_class_cats($classes) {
      
    global $post;
    foreach((get_the_category($post->ID)) as $category) {
      $classes[] = $category->category_nicename;
      $classes[] = $category->ID;
      return $classes;
    }
  } // MYTHEME_post_class_cats($classes)

?>