public static function setRankingKeys($url = false)
    {
        $xpath = self::_getXPath($url);
        $nodes = @$xpath->query("//*[@id='rank']/table/tr");

        if (5 == $nodes->length) {
            self::$_rankKeys = array(
                '1d' => 2,
                '7d' => 3,
                '1m' => 4,
                '3m' => 5,
            );
        }
        else if (4 == $nodes->length) {
            self::$_rankKeys = array(
                '1d' => 0,
                '7d' => 2,
                '1m' => 3,
                '3m' => 4,
            );
        }
        else if (3 == $nodes->length) {
            self::$_rankKeys = array(
                '1d' => 0,
                '7d' => 0,
                '1m' => 2,
                '3m' => 3,
            );
        }
        else if (2 == $nodes->length) {
            self::$_rankKeys = array(
                '1d' => 0,
                '7d' => 0,
                '1m' => 0,
                '3m' => 2,
            );
        }
    }