library/Rediska/Key/SortedSet.php
public function getRank($value, $revert = false)
    {
        return $this->_getRediskaOn()->getRankFromSortedSet($this->getName(), $value, $revert);
    }
public function getRank($value, $revert = false)
    {
        return $this->_getRediskaOn()->getRankFromSortedSet($this->getName(), $value, $revert);
    }
Get rank of member

@param integer $value  Member value
@param boolean $revert Revert elements (not used in sorting)
@return integer