xml - PHP SimpleXML. How to get the last item?

Question

How would I get the last item (or any specific item for that matter) in a simplexml object? Assume you don't know how many nodes there will be.

ex.

<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet type="text/xsl" href="/xsl.xml"?>
<obj 
  href="http://xml.foo.com/" 
  display="com.foo.bar" 
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
  xmlns="http://obix.org/ns/schema/1.0" 
>
 <list name="data" of="HistoryRecord">
  <obj>
   <abstime name="timestamp" val="1876-11-10T00:00:00-08:00"></abstime>
   <int name="energy_in_kwh" val="1234"></int>
   <int name="energy_out_kwh" val="123456"></int>
  </obj>
  <obj>
   <abstime name="timestamp" val="1876-11-10T00:15:00-08:00"></abstime>
   <int name="energy_in_kwh" val="1335"></int>
   <int name="energy_out_kwh" val="443321"></int>
  </obj>
 </list>
 <int name="count" val="2"></int>
</obj>

And I want to grab the last <obj></obj> chunk (or even just part of it).

Answer 1

Use XPath's last() function, which solves this very problem:

<?php 
$xml = simplexml_load_file('HistoryRecord.xml'); 
$xml->registerXPathNamespace('o', 'http://obix.org/ns/schema/1.0');

$xpath = "/o:obj/o:list/o:obj[last()]/o:int[@name = 'energy_in_kwh']";
$last_kwh = $xml->xpath($xpath); 
?> 

Here it looks for the last inner <obj>, and therein for the <int> with the name of "energy_in_kwh".

Watch out for the namespace registration. (All your elements are part of the "http://obix.org/ns/schema/1.0" namespace, the XPath query must reflect that.

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EDIT: Note that [last()] is equivalent to [position() = last()].