Remove a child with a specific attribute, in SimpleXML for PHP


Question

I have several identical elements with different attributes that I'm accessing with SimpleXML:

<data>
    <seg id="A1"/>
    <seg id="A5"/>
    <seg id="A12"/>
    <seg id="A29"/>
    <seg id="A30"/>
</data>

I need to remove a specific seg element, with an id of "A12", how can I do this? I've tried looping through the seg elements and unsetting the specific one, but this doesn't work, the elements remain.

foreach($doc->seg as $seg)
{
    if($seg['id'] == 'A12')
    {
        unset($seg);
    }
}
1
48
11/4/2008 5:56:28 PM

Accepted Answer

While SimpleXML provides a way to remove XML nodes, its modification capabilities are somewhat limited. One other solution is to resort to using the DOM extension. dom_import_simplexml() will help you with converting your SimpleXMLElement into a DOMElement.

Just some example code (tested with PHP 5.2.5):

$data='<data>
    <seg id="A1"/>
    <seg id="A5"/>
    <seg id="A12"/>
    <seg id="A29"/>
    <seg id="A30"/>
</data>';
$doc=new SimpleXMLElement($data);
foreach($doc->seg as $seg)
{
    if($seg['id'] == 'A12') {
        $dom=dom_import_simplexml($seg);
        $dom->parentNode->removeChild($dom);
    }
}
echo $doc->asXml();

outputs

<?xml version="1.0"?>
<data><seg id="A1"/><seg id="A5"/><seg id="A29"/><seg id="A30"/></data>

By the way: selecting specific nodes is much more simple when you use XPath (SimpleXMLElement->xpath):

$segs=$doc->xpath('//seq[@id="A12"]');
if (count($segs)>=1) {
    $seg=$segs[0];
}
// same deletion procedure as above
52
5/23/2017 11:47:13 AM

Contrary to popular belief in the existing answers, each Simplexml element node can be removed from the document just by itself and unset(). The point in case is just that you need to understand how SimpleXML actually works.

First locate the element you want to remove:

list($element) = $doc->xpath('/*/seg[@id="A12"]');

Then remove the element represented in $element you unset its self-reference:

unset($element[0]);

This works because the first element of any element is the element itself in Simplexml (self-reference). This has to do with its magic nature, numeric indices are representing the elements in any list (e.g. parent->children), and even the single child is such a list.

Non-numeric string indices represent attributes (in array-access) or child-element(s) (in property-access).

Therefore numeric indecies in property-access like:

unset($element->{0});

work as well.

Naturally with that xpath example, it is rather straight forward (in PHP 5.4):

unset($doc->xpath('/*/seg[@id="A12"]')[0][0]);

The full example code (Demo):

<?php
/**
 * Remove a child with a specific attribute, in SimpleXML for PHP
 * @link http://stackoverflow.com/a/16062633/367456
 */

$data=<<<DATA
<data>
    <seg id="A1"/>
    <seg id="A5"/>
    <seg id="A12"/>
    <seg id="A29"/>
    <seg id="A30"/>
</data>
DATA;


$doc = new SimpleXMLElement($data);

unset($doc->xpath('seg[@id="A12"]')[0]->{0});

$doc->asXml('php://output');

Output:

<?xml version="1.0"?>
<data>
    <seg id="A1"/>
    <seg id="A5"/>

    <seg id="A29"/>
    <seg id="A30"/>
</data>

Licensed under: CC-BY-SA with attribution
Not affiliated with: Stack Overflow
Icon