Cannot add text node within foreach loop

[ctcudd]

I'm stumped...

I am trying to write the contents of an array to an xml file.

 

I want the xml file to look similar to this

 

<chart>

  <chart_data>

    <row>

      <null/>

      <string>TCC</string>

      <string>TED</string>

      <string>HYJ</string>

      <string>HBA</string>

      <string>NDM</string>

    </row>

    <row>

      <string>work_completes</string>

      <number>4</number>

      <number>3</number>

      <number>1</number>

      <number>1</number>

      <number>1</number>

    </row>

  </chart_data>

</chart>

 

 

I am using the following code:

$doc = new DOMDocument();
  $doc->formatOutput = true;
  
  $chart = $doc->createElement( "chart" );
  $doc->appendChild( $chart );

  $chart_data = $doc->createElement( "chart_data" );
  $chart->appendChild( $chart_data);
  
  $row = $doc->createElement( "row" );
  $chart_data->appendChild( $row);
  
  $string = $doc->createElement( "null" );
  $row->appendChild( $string);
  
  foreach( $tests as $test )
  {
  $string = $doc->createElement( "string" );
  
  $author = $doc->createElement( "string" );
  $author->appendChild(
  $doc->createTextNode( $test['login'] )
  
  );

  $row->appendChild( $author );
  
  
  $title = $doc->createElement( "string" );
  $title->appendChild(
  $doc->createTextNode( $test['login'] )
  );
  $row->appendChild( $title );
  
  $publisher = $doc->createElement( "string" );
  $publisher->appendChild(
  $doc->createTextNode( $test['wc'] )
  );
  $row->appendChild( $publisher );
  
  }
  
  $row = $doc->createElement( "row" );
  $chart_data->appendChild( $row);
  
  $string = $doc->createElement( "null" );
  $row->appendChild( $string);
  
  echo $doc->saveXML();
$doc->save("test.xml"); 

 

 

and I am getting this in my xml file:

 

<chart>

  <chart_data>

    <row>

      <null/>

    </row>

    <row>

      <null/>

    </row>

  </chart_data>

</chart>

 

 

The contents of the arrary that I am using ($test) is:

{ ["TCC"]=>  int(4) ["TED"]=>  int(3) ["HYJ"]=>  int(2) ["HBA"]=>  int(1) ["NDM"]=>  int(1) }

 

It seems like my script is failing to create an element but only inside the foreach loops.  Greatly appreciate any  help I can get.  Thanks in advance