PHP Associative array to tree

tree.php

<?php

// Converts an array of single rows with a parent id column into a tree

function tree($rows){
	// supplied array must be indexed by row id
  $tree = array();  //stores the tree
  $tree_index = array();  //an array used to quickly find nodes in the tree
  $id_column = "id";  //The column that contains the id of each node
  $parent_column = "parent";  //The column that contains the id of each node's parent
   
  //build the tree - this will complete in a single pass if no parents are defined after children
  while(count($rows) > 0){
    foreach($rows as $row_id => $row){
      if($row[$parent_column]){
        if((!array_key_exists($row[$parent_column], $rows)) and (!array_key_exists($row[$parent_column], $tree_index))){
           unset($rows[$row_id]);
        }
        else{
          if(array_key_exists($row[$parent_column], $tree_index)){
            $parent = & $tree_index[$row[$parent_column]];
            $parent['children'][$row_id] = array("node" => $row, "children" => array());
            $tree_index[$row_id] = & $parent['children'][$row_id];
            unset($rows[$row_id]);
          }
        }
      }
      else{
        $tree[$row_id] = array("node" => $row, "children" => array());
        $tree_index[$row_id] = & $tree[$row_id];
        unset($rows[$row_id]);
      }
    }
  }
   
  //we are done with index now so free it
  unset($tree_index);
  
  return($tree);	

}

?>