ho realizzato uno script che funziona... prende tutte le parole, conta quelle uguali e fa quello che deve fare
però ho 2 problemi:
1) vorrei considerare solo il contenuto di un tag td specifico
2) vorrei poter confrontare dove nella pagina ci sono due parole di una frase uguali oppure addirittura tutte le frasi uguali presenti e non le parole...

vi posto lo script che cmq funziona e può servire a qualcuno....
Codice PHP:
<?phpini_set('max_execution_time',3000);$url = $_POST['url'];$result = getUrltext($url);
$bcheck = true;while ($bcheck) {    $delString = getStrContent("<script", "</script>", $result);    //echo $delString;    if ($delString != '') {        $result = str_replace("<script" . $delString . "</script>", '', $result);    }else{        $bcheck = false;    }}
$bcheck = true;while ($bcheck){    $delString = getStrContent("<style","</style>",$result);    if ($delString != '') {        $result = str_replace("<style" . $delString . "</style>", '', $result);    }else{        $bcheck = false;    }}
$bcheck = true;while ($bcheck){    $delString = getStrContent("<",">",$result);    if ($delString != '') {        $result = str_replace( "<" .$delString . ">", ' ', $result);
    }else{        $bcheck = false;    }}
$result = str_replace("\n",'',$result);$result = str_replace("\t",'',$result);$result = preg_replace("/[ #\&\+\-%@=\/\\\:;,\.'\"\^`~\_|\!\?\*$#<>()\[\]\{\}]/i", ' ', $result);$valueList1 = array();$valueList2 = array();$valresult = array();
$valueList1 = explode(' ',$result);$valueList1 = array_filter($valueList1);$valueList2 = $valueList1;$valueList1 = array_unique($valueList1);
foreach($valueList1 as $value1){    $ncount = 0;    foreach($valueList2 as $value2){        if($value1 == $value2){            $ncount++;        }    }    if($ncount > 4 && strlen($value1) > 4){        $value['name'] = $value1;        $value['count'] = $ncount;        array_push($valresult,$value);            }
}
foreach($valresult as $key => $row){    $volume[$key]  = $row['count'];}array_multisort($volume, SORT_DESC, $valresult);

function getUrltext($url, $encoding = true)  {        //ini_set('max_execution_time', 300);        //set_time_limit (300);        $ch = curl_init();        $headers = array('User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.116 Safari/537.36');        curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);        //curl_setopt($ch, CURLOPT_HTTPPROXYTUNNEL, 0);        /*curl_setopt($c, CURLOPT_PROXYTYPE, 'HTTP');        curl_setopt($ch, CURLOPT_PROXY, '92.114.43.122');        curl_setopt($ch, CURLOPT_PROXYPORT, '8080');        */        curl_setopt($ch,  CURLOPT_URL, $url);        //curl_setopt($ch, CURLOPT_ENCODING ,"windows-1251");        curl_setopt ($ch, CURLOPT_HEADER, 0);        curl_setopt($ch,  CURLOPT_RETURNTRANSFER, true);        //curl_setopt($ch, CURLOPT_COOKIEJAR,COOKIE);        //curl_setopt($ch,CURLOPT_COOKIEFILE,COOKIE);        curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);        $result = curl_exec($ch);        if($encoding)            $result  = mb_convert_encoding($result,"utf-8","windows-1251");        curl_close ($ch);        return $result;  }
function getStrContent($startText ,$endText, $strContent){    $strContent = stristr($strContent, $startText);    $strContent = substr($strContent, strlen($startText));    $stop = stripos($strContent,$endText);    $strContent = substr($strContent,0,$stop);    return $strContent;}?>
<table>    <?php        foreach($valresult as $item){            echo "<tr><td>" . $item['name'] . "</td><td>" . $item['count'] . "</td></tr>";        }    ?></table>


grazie a chi saprà aiutarmi