class Threaded_comments
{
 
    public $children = array();
	public $top;
 
    /**
     * @param array $comments
     */
    function __construct($comments)
    {
        foreach ($comments as $comment)
        {
                $this->children[$comment['parent_id']][] = $comment;
        }
    }
 
    /**
     * @param array $comment
     * @param int $depth
     */
    private function format_comment($comment, $depth)
    {
        for ($depth; $depth > 0; $depth--)
        {
            echo "\t";
        }
 
        echo $comment['text'];
        echo "\n";
    }
 
    /**
     * @param array $comment
     * @param int $depth
     */
    private function print_parent($comment, $depth = 0)
    {
        foreach ($comment as $c)
        {
            $this->format_comment($c, $depth);
 
            if (isset($this->children[$c['id']]))
            {
                $this->print_parent($this->children[$c['id']], $depth + 1);
            }
        }
    }
 
    public function print_comments()
    {
        foreach ($this->children[0] as $c)
        {
            if (isset($this->children[$c['id']]))
            {
                $this->print_parent($this->children[$c['id']]);
            }
        }
    }
 
}
 
 
$comments = array(array('id'=>1, 'parent_id'=>0,   'text'=>'top'),
		  array('id'=>2, 'parent_id'=>1,   'text'=>'Parent'),
                    array('id'=>3, 'parent_id'=>2,      'text'=>'Child'),
                    array('id'=>7, 'parent_id'=>2,      'text'=>'Child'),
                    array('id'=>4, 'parent_id'=>3,      'text'=>'Child Third level'),
                    array('id'=>5, 'parent_id'=>1,   'text'=>'Second Parent'),
                    array('id'=>6, 'parent_id'=>5,   'text'=>'Second Child')
                );
 
 
for ($foo=0;$foo<20000;$foo++)
{
$start = microtime(true);
 
$threaded_comments = new Threaded_comments($comments);
 
$threaded_comments->print_comments();
 
 
$end = microtime(true);
$sum += ($end-$start);
}
$average = $sum / 20000;