Reorder a nested HTML list in PHP

Recently I was working on website where I had to re-order a nested list (part of a navigation menu) – unfortunately I only had access to fragment of HTML so I couldn’t just manipulate the arrays from which it was built. The menu was compiled from various arrays and months within years sometimes came out all wrong.

So I thought, I’d just treat it as a bit of XML (which obviously it is) and re-order it using PHPs native XML handling classes. XML is one of those things that I use frequently, but never really do anything with, and finding a solution took me rather longer than I had expected. It is a mixture of simpleXML and XMLDom.

One of the main problems was the lack any real examples.

If anyone can suggest a more elegant solution, I would love to hear it.

Here is my code:

The UL to re-order

As you can see the month names are in the wrong order

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<ul id="menu">
    <li class="first"><a href="/news/q/date/2011/">2011</a></li>
    <li class="current last">
        <a href="/news/q/date/2010/">2010</a>
            <ul>
                <li class=""><a href="/news/q/date/2010/07/">July</a></li>
                <li class=""><a href="/news/q/date/2010/06/">June</a></li>    
                <li class=""><a href="/news/q/date/2010/11/">November</a></li>
                <li class=" last"><a href="/news/q/date/2010/10/">October</a></li>
                <li class=""><a href="/news/q/date/2010/09/">September</a></li>
                <li class=""><a href="/news/q/date/2010/08/">August</a></li>
                <li class="first"><a href="/news/q/date/2010/12/">December</a></li>
                <li class=""><a href="/news/q/date/2010/05/">May</a></li>
           </ul>
    </li>
</ul>

My (woeful) solution

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$xml = simplexml_load_string($string);
 
// pull a node tree as an Array out using simpleXML xpath
$trees = $xml->xpath('/ul/li/ul');
 
$array = array();
$order = array();
 
$i = 0;
 
// we only need to delve into XML if there are any nested <ul>s
if(isset($trees[0])){
 
	foreach($trees[0] as $var){
 
		// store each node in an indexed array
		$array[$i] = $var; 
		// store the month number in an index array
		// based on the text node value of the <a> tag
		$order[$i] = date('m', strtotime((string) $var->a)); 
 
		$i++;
	}
 
	// sort the month number array descending, but maintaining the keys
	arsort($order); 
 
	// create a new XML Dom object to manipulate stuff
	$dom = new DomDocument();
	// create a holder node <ul>
	$ul = $dom->createElement('ul');
 
	// iterate through the array of simpleXML objects 
	// based on the order in which their keys appear in the re-ordered array
	foreach($order as $key => $value){
		// get the simpleXML objects into a string
		$node = dom_import_simplexml($array[$key]);
		// get the string into an actual DOM node
		$node = $dom->importNode($node, true);
		// append
		$ul->appendChild($node);	
	}
 
	//$dom->appendChild($ul);
 
	// unset the contents of the original <ul> node that we have resorted
	$parent = $trees[0]->xpath( 'parent::*' );
	$parent[0]->ul = NULL;
 
	// turn our simpleXML object into a DOM object
	$ixml = dom_import_simplexml($xml);
	$new = new DOMDocument('1.0');
	$ixml = $new->importNode($ixml, true);
	$ixml = $new->appendChild($ixml);
 
	// fire up a DOM xpath object
	$xpath = new DomXpath($new);
	// pull a node tree out using simpleXML xpath
	$tree = $xpath->query('/ul/li/ul');
 
	// add our newly created DOM node conatining the re-ordered <ul> after the existing node
	$tree->item(0)->parentNode->appendChild($new->importNode($ul, true));
	// delete the original empty node
	$tree->item(0)->parentNode->removeChild($tree->item(0));
 
	echo $new->saveHTML();
 
} else {
 
	echo $string;
 
}