public function groupValue($value, $idSite)
    {
        switch ($this->type) {
            case Dimension::TYPE_URL:
                return str_replace(array('http://', 'https://'), '', $value);
            case Dimension::TYPE_BOOL:
                return !empty($value) ? '1' : '0';
            case Dimension::TYPE_DURATION_MS:
                return number_format($value / 1000, 2); // because we divide we need to group them and cannot do this in formatting step
        }
        return $value;
    }