how to use the sum-function in xpath? - php

Question

There's the sum-function in xpath:
<list>
<a>1</a>
<a>3</a>
<a>4</a>
</list>
Now with SimpleXml...
var_dump($xml->xpath("sum(/list/a)"));
delivers NULL instead of 8
What's wrong here?
see it not working: https://eval.in/135558
EDIT: I've used this workaround for SimpleXml to avoid iterating:
$sum = $xml->xpath("/list/a");
$sum = array_sum(array_walk("intval", $sum));

Answer 1

If you're using SimpleXML, you're going to have to do it manually. However, you can use DOMDocument to achieve this. Just use evaluate() method to evaluate the XPath expression:
$dom = new DOMDocument;
$dom->loadXML($xml); // $xml is the XML string
$xpath = new DOMXPath($dom);
$sum = (int) $xpath->evaluate('sum(/list/a)'); // => 8
Demo
SimpleXML solution:
$xml = simplexml_load_string($xml);
$sum = 0;
foreach ($xml->a as $node) {
$sum += (int) $node;
}
echo $sum; // => 8
Demo

Answer 2

Use DOMXPath::evaluate() here:
$str = <<<XML
<list>
<a>1</a>
<a>3</a>
<a>4</a>
</list>
XML;
$output = new SimpleXMLElement($str);
$doc = new DOMDocument();
$doc->loadXML($str);
$selector = new DOMXPath($doc);
var_dump($selector->evaluate('sum(//list/a/text())'));
// double(8)
Side-note: It will return a double not an integer. This might be surprising in the first place.