<?php
// Extract Tag
function extractCommonWords($string){
      $stopWords = array('i','a','about','an','and','are','as','at','be','by','com','de','en','for','from','how','in','is','it','la','of','on','or','that','the','this','to','was','what','when','where','who','will','with','und','the','www');
   
      $string = preg_replace('/\s\s+/i', '', $string); // replace whitespace
      $string = trim($string); // trim the string
      $string = preg_replace('/[^a-zA-Z0-9 -]/', '', $string); // only take alphanumerical characters, but keep the spaces and dashes too…
      $string = strtolower($string); // make it lowercase
   
      preg_match_all('/\b.*?\b/i', $string, $matchWords);
      $matchWords = $matchWords[0];
      
      foreach ( $matchWords as $key=>$item ) {
          if ( $item == '' || in_array(strtolower($item), $stopWords) || strlen($item) <= 5 ) {
              unset($matchWords[$key]);
          }
      }   
      $wordCountArr = array();
      if ( is_array($matchWords) ) {
          foreach ( $matchWords as $key => $val ) {
              $val = strtolower($val);
              if ( isset($wordCountArr[$val]) ) {
                  $wordCountArr[$val]++;
              } else {
                  $wordCountArr[$val] = 1;
              }
          }
      }
      arsort($wordCountArr);
      $wordCountArr = array_slice($wordCountArr, 0, 10);
      return $wordCountArr;
}
?>