I have an xml file that I'm parsing with php's simplexml, but I'm having an issue with an iteration through nodes.

the xml:

<channel>
<item>
<title>Title1</title>
<category>Cat1</category>
</item>
<item>
<title>Title2</title>
<category>Cat1</category>
</item>
<item>
<title>Title3</title>
<category>Cat2</category>
</item>
</channel>

my counting function:

public function cat_count($cat){
    $count = 0;
    $items = $this->xml->channel->item;
    $size = count($size);

    for($i=0;$i<$size;$i++){
        if($items[$i]->category == $cat){
            $count++;
        }
    }
    return $count;
}

Am I overlooking an error in my code, or is there another preferred method for iterating through the nodes? I've also used a foreach and while statement with no luck, so I'm at a loss. Any suggestions?