Recursive Algorithm in PHP

The Corinthian

I have a an array that essentially hangs off itself (each element has an ID and parent ID that references another element) and I want to be able to out put the tree that this produces in an XML format.

Needless to say writing an algorithm to do this from scratch would be a serious pain in the arse and I've already STFW with limited success, so if anyone has a ready-made function(s) or can point me to a resource that would make my life easier, I'd greatly appreciate it.

Evil Phil

Post some code that generates the array and I'm sure somebody will have a go.

The Corinthian

Pretty straightforward - one could suggest the following:
[PHP]
$a_MyArray = array(
array("id" => 1, "name" => "A", "parentid" => 0),
array("id" => 2, "name" => "B", "parentid" => 0),
array("id" => 3, "name" => "C", "parentid" => 1),
array("id" => 4, "name" => "D", "parentid" => 1),
array("id" => 5, "name" => "E", "parentid" => 2),
array("id" => 6, "name" => "F", "parentid" => 4)
);
[/PHP]
And what I'm looking to get back is something like:

<node name="A" id="1">
    <node name="C" id="3" />
    <node name="D" id="4">
        <node name="F" id="6" />
    </node>
</node>
<node name="B" id="2">
    <node name="E" id="5" />
</node>

Baring in mind nodes can continue to the Nth level.

oeb

What you are doing there is known as a Linked List in languages that support it. There are implimentations in php (such as http://www.phpclasses.org/browse/file/7143.html) but I have not looked into them too much. Most classes like this will have some kind of iterate() function, and the handling there should be similar to what you are looking for.

seamus

I remember writing a function which converted a flat array into a tree-style multidimensional array. I'll see if I can dig it out and see if it's any use to you.

ron_darrell

This might need a bit of tweaking but give it a try:

<?php
function subnode($parentid, $array)
{
	$i = $parentid;
	while($i < sizeof($array))
	{
		if($array[$i].parentid == $parentid)
		{
			echo "<node name=\"".$array[$i].name."\" id=\"".$array[$i].id."\" >";
			subnode($array[$i].id, $i, $array);
			echo "</node>";
		}
		$i++;		
	}
}

$j = 0;
while($j < sizeof($a_MyArray))
{
       if($a_MyArray[$j].parentid == 0)
       {
               subnode($a_MyArray[$j].id, $a_MyArray);
       }
       $j++;
}
?>

Unfortunately, I don't have an apache server to hand to test this so as I said you might need to tweak it but the logic should hold. If not at least it's a pointer in the right(ish) direction

Regards,
RD