Array to xml - issue with repeated tags

Question

EDITED
I'm trying to put my form inputs into an xml file.

Searching on this site I've found the following code and I used it to parse $_POST content.

After a few attempts I realized that "numeric tags" (resulting from not-associative arrays) could be reason of my insuccess so I modified the code as below:

function array_to_xml(array $arr, SimpleXMLElement $xml, $NumK = false)
{
    foreach ($arr as $k => $v) {
        if (is_array($v)){
            preg_match('/^0|[1-9]\d*$/', implode(array_keys($v)))
            ? array_to_xml($v, $xml->addChild($k), true)
            : array_to_xml($v, $xml->addChild($k));
        }else{
            $NumK
            ? $xml->addChild('_'.$k.'_', $v)
            : $xml->addChild($k, $v);
        }
    }
    return $xml;
}

Anyway I'm still "fighting" with xpath commands because I'm not able to find the GrandParent of some nodes (coming from not-associative arrays) that I need to convert into repeated tags.

That's the logic I'm trying to follow:
1st - Find nodes to reformat (The only ones having numeric tag);
2nd - Find grandparent (The tag I need to repeat);
3rd - Replace the grandparent (and his descendants) whith a grandparent's tag for each group of grandchilds (one for each child).

So far I'm still stuck on 1st step beacuse of xpath misunderstanding.

Below, the result xml I have and how I would to transform it:

My array is something like:

$TestArr = Array
    ("First" => array
        ("Martha" => "Text01"
        ,
        "Lucy" => "Text02"
        ,
        "Bob" => array 
            ("Jhon" => array
                ("01", "02")
            ),
        "Frank" => "One"
        ,
        "Jessy" => "Two"
        )
    ,
    "Second" => array
        ("Mary" => array 
            ("Jhon" => array
                ("03", "04")
            ,
            "Frank" => array
                ("Three", "Four")
            ,
            "Jessy" => array
                ("J3", "J4")
            )
        )
    );

using the function array_to_xml($TestArr, new SimpleXMLElement('<root/>')) I get an xml like:

<root>
    <First>
        <Martha>Text01</Martha>
        <Lucy>Text02</Lucy>
        <Bob>
            <Jhon>
                <_0_>01</_0_>
                <_1_>02</_1_>
            </Jhon>
        </Bob>
        <Frank>One</Frank>
        <Jessy>Two</Jessy>
    </First>
    <Second>
        <Mary>
            <Jhon>
                <_0_>03</_0_>
                <_1_>04</_1_>
            </Jhon>
            <Frank>
                <_0_>Three</_0_>
                <_1_>Four</_1_>
            </Frank>
            <Jessy>
                <_0_>J3</_0_>
                <_1_>J4</_1_>
            </Jessy>
        </Mary>
    </Second>
</root>

My needed result is something like:

<root>
    <First>
        <Martha>Text01</Martha>
        <Lucy>Text02</Lucy>
            <Bob>
                <Jhon>01</Jhon>
            </Bob>
            <Bob>
                <Jhon>02</Jhon>
            </Bob>
        <Frank>One</Frank>
        <Jessy>Two</Jessy>
    </First>
    <Second>
        <Mary>
            <Jhon>03</Jhon>
            <Frank>Three</Frank>
            <Jessy>J3</Jessy>
        </Mary>
        <Mary>
            <Jhon>04</Jhon>
            <Frank>Four</Frank>
            <Jessy>J4</Jessy>
        </Mary>
    </Second>
</root>

Answer 1

I've updated the code to try and get closer to what you were trying to achieve. I've taken into the account of how to identify the grouping of data and to do this I've added an 'id' attribute to each of the elements added in this way. Also for convenience, I set a 'max' counter for the parent elements.

The first XPath expression (//*[@id]/..) fetches all the elements that needed to be processed. This then loops for the number of sub elements counted earlier. The XPath descendant::*[@id='{$i}'] picks out each set of elements (so all ones with id='0', then '1' etc.) This is the natural grouping of the data.

function array_to_xml(array $arr, SimpleXMLElement $xml, string $elementName = null)
{
    foreach ($arr as $k => $v) {
        if (is_array($v)){
            if ( preg_match('/^0|[1-9]\d*$/', implode(array_keys($v)))) {
                array_to_xml($v, $xml, $k);
            }
            else    {
                array_to_xml($v, $xml->addChild($k));
            }
        }
        else    {
            if ( $elementName != null )   {
                $newElement = $xml->addChild($elementName, $v);
                $newElement["id"] = $k;
                $xml["max"] = $k;
            }
            else    {
                $xml->addChild($k, $v);
            }
        }
    }
    //return $xml;
}
$xml = new SimpleXMLElement("<root />");
array_to_xml($TestArr, $xml);
$todoList = $xml->xpath("//*[@id]/..");
foreach ( $todoList as $todo )  {
    $parent = $todo->xpath("..")[0];
    for ( $i = 0; $i <= $todo['max']; $i++ )    {
        $content = $todo->xpath("descendant::*[@id='{$i}']");
        $newName = $todo->getName();
        $new = $parent->addChild($newName);
        foreach ( $content as $addIn )  {
            $new->addChild($addIn->getName(), (string)$addIn);
        }
    }
    unset ( $parent->$newName[0]);
}

print $xml->asXML(); 

Outputs...

<?xml version="1.0"?>
<root>
    <First>
        <Martha>Text01</Martha>
        <Lucy>Text02</Lucy>
        <Frank>One</Frank>
        <Jessy>Two</Jessy>
        <Bob>
            <Jhon>01</Jhon>
        </Bob>
        <Bob>
            <Jhon>02</Jhon>
        </Bob>
    </First>
    <Second>
        <Mary>
            <Jhon>03</Jhon>
            <Frank>Three</Frank>
            <Jessy>J3</Jessy>
        </Mary>
        <Mary>
            <Jhon>04</Jhon>
            <Frank>Four</Frank>
            <Jessy>J4</Jessy>
        </Mary>
    </Second>
</root>

Answer 2

Iterate your array value and add elements with the same key

if (is_array($v)){
    foreach($v as $arr_ele){
        $xml->addChild($k, $arr_ele);
    }
}