如何在PHP中组合XML中的列表

I Have a Parts List Coming from an XML File, It goes something like what is below. I Want to be able to generate using PHP a Combined List. For Example the "Part 1" Is recorded twice. I want the Qty to Show 13 Under Part 1 when Generated either in a JSON output or another XML Output. What would be the best way of doing that? I looked at the php function array_combine but wasn't able to figure out if the values could be combined mathematically instead of showing one of the results. I am loading the XML from a url in simplexml_load_file() function. Thank You for your help

My XML from URL:

   <db>
      <record>
         <part>Part 1</part>
         <qty>4</qty
      </record>
    <record>
         <part>Part 2</part>
         <qty>5</qty
    </record>
    <record>
         <part>Part 1</part>
         <qty>9</qty
    </record>
  </db>

Want to Display:

   <db>
      <record>
         <part>Part 1</part>
         <qty>13</qty>
      </record>
    <record>
         <part>Part 2</part>
         <qty>5</qty
    </record>
  </db>

Iterate over the XML document, accumulating part quantities as you go:

$simpleXmlElement = new SimpleXMLElement(<<<XML
<db>
    <record>
        <part>Part 1</part>
        <qty>4</qty>
    </record>
    <record>
        <part>Part 2</part>
        <qty>5</qty>
    </record>
    <record>
        <part>Part 1</part>
        <qty>9</qty>
    </record>
</db>
XML
);

$quantities = array();
foreach ($simpleXmlElement as $child) {
    if ($child->part && $child->qty) {
        $part = (string)$child->part;
        if (!isset($quantities[$part])) {
            $quantities[$part] = 0;
        }
        $quantities[$part] += (int)$child->qty;
    }
}
echo json_encode($quantities);

simplexml_load_string() will parse the xml and build an array of all the records as 'record' => array(...)

you can then iterate the record array and group them by type

$parts = array();
foreach ($document['record'] as $item) {
    if (isset($parts[$item['part']]) $parts[$item['part']] += $item['qty'];
    else $parts[$item['part']] = $item['qty'];
}

after the above loop, $parts will contain a hash mapping the part name to qty