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I need more control over the category listing output, so I'm using get_categories (http://codex.wordpress.org/Function_Reference/get_categories), instead of wp_list_categories (http://codex.wordpress.org/Template_Tags/wp_list_categories).

This function returns a flat array of objects ordered by a certain attribute. How can I build a hierarchical list from it like wp_list_categories() does?

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up vote 4 down vote accepted

The most ideal solution for walking over the data is to use the WordPress walker class.


You won't find many an example around the web for using it, but one was given by Scribu here.


You can also look to the classes WordPress uses to extend the walker as further examples.


Hope that helps..

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thanks, I ended up creating my own walker.. – Alex Nov 20 '10 at 18:21
You're welcome.. :) – t31os Nov 20 '10 at 22:54

how to build a hierarchical tree from get_categories

see: http://stackoverflow.com/questions/3287603/wordpress-wp-list-categories-problem

in that answer Jan Fabry Jan Fabry jan-fabry jan-fabry does it like this:

$categories = get_categories();

// First index all categories by parent id, for easy lookup later
$cats_by_parent = array();
foreach ($categories as $cat)
  $parent_id = $cat->category_parent;
  if (!array_key_exists($parent_id, $cats_by_parent)) 
    $cats_by_parent[$parent_id] = array();
  $cats_by_parent[$parent_id][] = $cat;

// Then build a hierarchical tree
$cat_tree = array();
function add_cats_to_bag(&$child_bag, &$children)
   global $cats_by_parent;
   foreach ($children as $child_cat) 
     $child_id = $child_cat->cat_ID;
     if (array_key_exists($child_id, $cats_by_parent)) 
        $child_cat->children = array();
        add_cats_to_bag($child_cat->children, $cats_by_parent[$child_id]);
     $child_bag[$child_id] = $child_cat;
add_cats_to_bag($cat_tree, $cats_by_parent[0]);
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