Php xml，用xml对象替换正在使用的节点

I'm facing an Xml problem. Probably something stupid but I can't see it...

Here is my Xml at start :

<combinations nodeType="combination" api="combinations">
    <combination xlink:href="http://localhost:8888/vmv/ps/api/combinations/1">
        <id><![CDATA[1]]></id>
    </combination>
    <combination xlink:href="http://localhost:8888/vmv/ps/api/combinations/2">
        <id><![CDATA[2]]></id>
    </combination>
</combinations>

So for each node, I make the API call then I want to replace the node by the returned value, like that :

$c_index = 0;
foreach($combinations->combination as $c){
    $new = apiCall($c->id); //load the new content
    $combinations->combination[$c_index] = $new;
    $c_index++;
}

If I dump the $new into the foreach, I got an simplexmlobject which is fine but if I dump the $combinations->combination[$x], I've got big string of blank...

I'd like to get :

<combinations nodeType="combination" api="combinations">
    <combination xlink:href="http://localhost:8888/vmv/ps/api/combinations/1">
        <my new tree>
            ....
        </my new tree>
    </combination>
    <combination xlink:href="http://localhost:8888/vmv/ps/api/combinations/2">
        <my new tree>
            ....
        </my new tree>
    </combination>
</combinations>

I must be missing something but what...? That's the question...

thanks for your help !

You can change the current element $c of the foreach iteration by making use of a so called SimpleXMLElement-self-reference. By the magic nature of the SimpleXMLElement the entry for both array-access or property access of the number 0 (zero) represents the element itself. This can be used to change the elements value for example:

foreach ($combinations->combination as $c) {
    $new  = apiCall($c->id); //load the new content
    $c[0] = $new;
}

The important part is $c[0] here. You could also write $c->{0} for property access with numbers. Example output (may api call returns "apiCall($paramter)" as string):

<combinations nodeType="combination" api="combinations">
    <combination xlink:href="http://localhost:8888/vmv/ps/api/combinations/1">apiCall('1')</combination>
    <combination xlink:href="http://localhost:8888/vmv/ps/api/combinations/2">apiCall('2')</combination>
</combinations>

The example in full:

$buffer = <<<XML
<root xmlns:xlink="ns:1">
    <combinations nodeType="combination" api="combinations">
        <combination xlink:href="http://localhost:8888/vmv/ps/api/combinations/1">
            <id><![CDATA[1]]></id>
        </combination>
        <combination xlink:href="http://localhost:8888/vmv/ps/api/combinations/2">
            <id><![CDATA[2]]></id>
        </combination>
    </combinations>
</root>
XML;


function apiCall($string)
{
    return sprintf('apiCall(%s)', var_export((string)$string, true));
}

$xml = simplexml_load_string($buffer);

$combinations = $xml->combinations;

foreach ($combinations->combination as $c) {
    $new  = apiCall($c->id); //load the new content
    $c[0] = $new;
}

$combinations->asXML('php://output');