If you are creating a product import script for Magento, you probably need to generate on the fly all your category ids based on category names. Here is a situation where you can use this script. Your product feed contains a column called CATEGORY with values in this format: Girls>Infant>Basketball and Boys>Infant>Basketball If you want to assign products from those categories to your Magento categories Girls > Infant > Basketball and Boys > Infant > Basketball , then you have to get the category ids for Girls, boys, Infant and Basketball. Remember that Infant id for Boys is not the same as Girls.

<?php

function listArrayRecursive($someArray,$root) {
    $iterator = new RecursiveIteratorIterator(new RecursiveArrayIterator($someArray), RecursiveIteratorIterator::SELF_FIRST);
    foreach ($iterator as $k => $v) {
        if ($iterator->hasChildren()) {
        } else {
            for ($cat_ids = array(),$cats = array(), $i = 0, $z = $iterator->getDepth(); $i <= $z; $i++) {
	         if($i%2){
                    $cat_ids[] = $iterator->getSubIterator($i)->key();
		  }  else {
            	   $cats[] = $iterator->getSubIterator($i)->key();
            	}
            }
            $category_ids = implode(',', $cat_ids);
	    $category_names = implode(',', $cats);
            $output[ $category_names ] = $root.','.$category_ids;
        }
    }
    return $output;
}

function nodeToArray(Varien_Data_Tree_Node $node) {
		$result = array();
		if( is_object($node)) {
			$name = $node->getName();
			$result[$name] = $name;
			$result[$name] = array();
			if($node->hasChildren()){ 
				foreach ($node->getChildren() as $child) {
					$result[$name][$child->getId()] = nodeToArray($child);
				}
			} else {
				$result[$name] =  $name;
			}
		}
		return $result;
	}
	
	

function load_tree($parentId,$store) {
		$tree = Mage::getResourceSingleton('catalog/category_tree')->load();
		$root = $tree->getNodeById($parentId);

		if($root && $root->getId() == 1) {
			$root->setName(Mage::helper('catalog')->__('Root'));
		}

		$collection = Mage::getModel('catalog/category')->getCollection()->setStoreId($store)->addAttributeToSelect('name')->addAttributeToSelect('is_active');
		$tree->addCollectionData($collection, true);

		return nodeToArray($root);

	}