def median(self, values, axis=0, average=True):
        """compute the median value over each group.

        Parameters
        ----------
        values : array_like, [keys, ...]
            values to compute the median of per group
        axis : int, optional
            alternative reduction axis for values
        average : bool, optional
            when average is true, the average of the two central values is taken for groups with an even key-count

        Returns
        -------
        unique: ndarray, [groups]
            unique keys
        reduced : ndarray, [groups, ...]
            value array, reduced over groups
        """
        mid_2 = self.index.start + self.index.stop
        hi = (mid_2    ) // 2
        lo = (mid_2 - 1) // 2

        #need this indirection for lex-index compatibility
        sorted_group_rank_per_key = self.index.sorted_group_rank_per_key

        def median1d(slc):
            #place values at correct keys; preconditions the upcoming lexsort
            slc    = slc[self.index.sorter]
            #refine value sorting within each keygroup
            sorter = np.lexsort((slc, sorted_group_rank_per_key))
            slc    = slc[sorter]
            return (slc[lo]+slc[hi]) / 2 if average else slc[hi]

        values = np.asarray(values)
        if values.ndim>1:   #is trying to skip apply_along_axis somewhat premature optimization?
            values = np.apply_along_axis(median1d, axis, values)
        else:
            values = median1d(values)
        return self.unique, values
compute the median value over each group.

        Parameters
        ----------
        values : array_like, [keys, ...]
            values to compute the median of per group
        axis : int, optional
            alternative reduction axis for values
        average : bool, optional
            when average is true, the average of the two central values is taken for groups with an even key-count

        Returns
        -------
        unique: ndarray, [groups]
            unique keys
        reduced : ndarray, [groups, ...]
            value array, reduced over groups