Implementation of a Tree Structure in PHP – II

I received an excellent comment by ‘Chris Rogers’ on my earlier post Implementation of a Tree Structure in PHP. He commented to the fact that the iterator does not work if the child was created prior to the parent. Excellent catch!

To that end I have modified the class, specifically the iterator’s ‘createNode’ method which takes care of this fact. The final code can be found on Github: tree-php

 * JTreeRecursiveIterator
 * To use a recursive iterator you have to extend of the RecursiveIteratorIterator
 * As an example I have built an unordered list
 * For detailed information on please see RecursiveIteratorIterator
 * @package   JTree
 * @author Jayesh Wadhwani
 * @copyright Jayesh Wadhwani
 * @version 1.0 2011
class JTreeRecursiveIterator extends RecursiveIteratorIterator {
   * @var _jTree the JTree object
	private $_jTree;
   * @var _str string with ul/li string
	private $_str;

	 * JTreeRecursiveIterator::__construct()
	 * @param mixed $jt - the tree object
	 * @param mixed $iterator - the tree iterator
	 * @param mixed $mode
	 * @param integer $flags
	 * @return
	public function __construct(JTree $jt, $iterator, $mode = RecursiveIteratorIterator::LEAVES_ONLY, $flags = 0) {

		parent::__construct($iterator, $mode, $flags);
		$this->_jTree = $jt;
		$this->_str = "<ul>\n";

	 * JTreeRecursiveIterator::endChildren()
	 * Called when end recursing one level.(See manual)
	 * @return void
	public function endChildren() {
		$this->_str .= "</ul></li>\n";

	 * JTreeRecursiveIterator::callHasChildren()
	 * Called for each element to test whether it has children. (See Manual)
	 * @return mixed
	public function callHasChildren() {
		$ret = parent::callHasChildren();
		$value = $this->current()->getValue();

		if($ret === true) {
			$this->_str .= "<li>{$value}<ul>\n";
		} else {
			$this->_str .= "<li>{$value}</li>\n";
		return $ret;

	 * JTreeRecursiveIterator::__destruct()
	 * On destruction end the list and display.
	 * @return void
	public function __destruct() {
		$this->_str .= "</ul>\n";
      echo $this->_str;


Now if you were to re-arrange the array like so where I have made ‘Fires'(id=5) as a child of Hurricanes(id=9)

$categories = array();
$categories[] = array('id' => 1, 'weather_condition' => 'weather', 'parent_id' => 9999);
$categories[] = array('id' => 2, 'weather_condition' => 'Earthquakes', 'parent_id' => 1);
$categories[] = array('id' => 3, 'weather_condition' => 'Major', 'parent_id' => 2);
$categories[] = array('id' => 4, 'weather_condition' => 'Minor', 'parent_id' => 2);
$categories[] = array('id' => 5, 'weather_condition' => 'Fires', 'parent_id' => 9);
$categories[] = array('id' => 6, 'weather_condition' => 'Rain', 'parent_id' => 1);
$categories[] = array('id' => 7, 'weather_condition' => 'Flooding', 'parent_id' => 6);
$categories[] = array('id' => 8, 'weather_condition' => 'Washout', 'parent_id' => 6);
$categories[] = array('id' => 9, 'weather_condition' => 'Hurricanes', 'parent_id' => 1);

And run it

//create a new tree object
$jt = new JTree();

//iterate building the tree
foreach($categories as $category) {
   $uid = $jt->createNode($category['weather_condition'],$category['id'], $category['parent_id']);

//update: removed third variable. Use defaults 
$it = new JTreeRecursiveIterator($jt, new JTreeIterator($jt->getTree()));

//iterate to create the ul list
foreach($it as $k => $v) {}

Note that I have removed addChild. It is included in createNode.

The result being:

  • weather
    • Earthquakes
      • Major
      • Minor
    • Rain
      • Flooding
      • Washout
    • Hurricanes
      • Fires

Many thanks to Chris for pointing this out.

Happy computing!

13 thoughts on “Implementation of a Tree Structure in PHP – II

  1. Hi!
    Thanks for sharing your awesome work…
    I’m having trouble building a tree using data retrieved from mysql table.
    I’ve used the following code to store data into $categories array:

    mysql_connect(“localhost”, “user”, “pass”);
    $result = mysql_query(“SELECT id,name,parentId FROM webcats”);
    $categories = array();
    while ($row = mysql_fetch_assoc($result)) {
    $categories[] = $row;

    $jt = new JTree();
    foreach($categories as $category) {
    $uid = $jt->createNode($category[‘name’],$category[‘id’], $category[‘parentId’]);
    $it = new JTreeRecursiveIterator($jt, new JTreeIterator($jt->getTree()), true);
    foreach($it as $k => $v) {}

    The tree appears empty… What I’m doing wrong?

    Thanks for your time….


  2. Hi! I’m using your classes, but I have some problems with JTree->modifyNode (updating root node for linking to other existing node).
    Seems it dosn’t updates childrens information on parent node, it’s right?
    All works fine if I use createNode for update info



    • Hi Antonio,

      Yes, you are correct. It will not update the children’s info. All modifyNode() does is given the uid of a node(it fetches the actual node) it modifies the value and its parent’s uid. By changing the parent UID it allows you to move the node anywhere in the tree.

      Thank you



    • Hi Jonathan,

      Thanks for your question.

      The quickest way that comes to mind is to sort the children.
      So in the JtreeIterator class I would do this:

           * JTreeIterator::getChildren()
           * @return JTreeIterator
          public function getChildren() {
              $childObj = $this->_list[$this->key()];
              $children = $childObj->getChildren();
              usort($children, array($this, '_cmp'));
              return new JTreeIterator($this->_list, $children);
          private function _cmp($a, $b)
              $a = strtolower($this->_list[$a]->getValue());
              $b = strtolower($this->_list[$b]->getValue());
              if ($a == $b) {
                  return 0;
              return ($a < $b) ? -1 : 1;

      You can tweak the functions to your liking. Give it a go and hopefully this gives you the desired results.



  3. Hi, I found, that multiple values can be inserted as string or array in first parameter of $jt->createNode,
    but is there a simple way to display first parent (id => 1, ‘weather_condition’ => ‘weather’… ) in ul list?


      • Hi Jayesh,
        thanks for that change with top parent, its great.

        And one thing what I notice:
        First item in array must be the parent of all items (tree root). Or only part of the tree will display.


    • If you are looking for an array which has an one-to-one correspondance to the tree then that will be difficult as both are different structures. On the other hand if you want to build a custom array for a specific task then that is not too difficult. Just initialize the array in the constructor for JTreeRecursiveIterator class and then replace the statements such as $this->_str = “html stuff”; with your specific code.

      Hope this helps.



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