Sorting XML File into ascending order using php [duplicate]

Answer 1

file '1.php':

load('books.xml');         //1. load books from xml to array
usort($arr, array('books','cmp'));  //2. sort array
$b->save('out.xml',$arr);           //3. save array to xml
?>

file 'books.php':

load($fname))  $res=$this->parse($doc);
        else                    throw new Exception('error load XML');

        return $res;
     }


     static public function cmp($a, $b)
     {
         if ($a['fields']['borrowedcount'] == $b['fields']['borrowedcount']) {
             return 0;
         }
         return ($a['fields']['borrowedcount'] < $b['fields']['borrowedcount']) ? -1 : 1;
     }


     private function parse($doc)
     {
        $xpath = new DOMXpath($doc);
        $items = $xpath->query("items/item");
        $result = array();
        foreach($items as $item)
        {
           $result[]=array('id'=>$item->getAttribute('id'), 'fields'=>$this->parse_fields($item));
        }
        return $result;
     }


     private function parse_fields($node)
     {
        $res=array();
        foreach($node->childNodes as $child)
        {
           if($child->nodeType==XML_ELEMENT_NODE)
           {
              $res[$child->nodeName]=$this->get_value($child);
           }
        }

        return $res;
     }

     private function get_value($node)
     {
        if($node->nodeName=='courses')
        { 
           $res=array();
           foreach($node->childNodes as $child)
           {
              if($child->nodeType==XML_ELEMENT_NODE)
              {
                 $res[]=$child->nodeValue;
              }
           } 
           return $res;
        }
        else
        {
           return $node->nodeValue;
        }
     }

     //save array to xml
     public function save($fname, $rows)
     {
        $doc = new DOMDocument('1.0','utf-8');
        $doc->formatOutput = true;

        $bc = $doc->appendChild($doc->createElement('bookcollection'));
        $items = $bc->appendChild($doc->createElement('items'));

        foreach($rows as $row)
        {
           $item=$items->appendChild($doc->createElement('item'));
           $item->setAttribute('id',$row['id']);
           foreach($row['fields'] as $field_name=>$field_value)
           {
              $f=$item->appendChild($doc->createElement($field_name));
              if($field_name=='courses')
              {
                 foreach($field_value as $course_val)
                 {
                    $course=$f->appendChild($doc->createElement('course'));
                    $course->appendChild($doc->createTextNode($course_val));
                 }
              }
              else
              {
                 $f->appendChild($doc->createTextNode($field_value));
              }

           }
        }

        file_put_contents($fname, $doc->saveXML());
     }

  }
?>