&$item) { $itemsByReference[$item['id']] = &$item; // Children array: $itemsByReference[$item['id']]['nodes'] = array(); } // Set items as children of the relevant parent item. foreach($data as $key => &$item) { //echo "

";print_r($itemsByReference[$item['parent_id']]);die;
	   if($item['parent_id'] && isset($itemsByReference[$item['parent_id']])) {
	      $itemsByReference [$item['parent_id']]['nodes'][] = &$item;
		}
	}
	// Remove items that were added to parents elsewhere:
	foreach($data as $key => &$item) {
		 if(empty($item['nodes'])) {
			unset($item['nodes']);
			}
	   if($item['parent_id'] && isset($itemsByReference[$item['parent_id']])) {
	      unset($data[$key]);
		 }
	}

	// Encode:
	echo json_encode($data);
	?>