protected function computeUsingFreqDist(array $tokens)
    {
        $freqDist = (new FreqDist($tokens))
            ->getKeyValuesByFrequency();
                
        foreach($freqDist as $token => $freqValue)
        {
            if(!isset($this->stopWords[$token])) {
                $this->stopWords[$token] = $freqValue;
            } else {
                $this->stopWords[$token] += $freqValue;
            }
        }        
    }