Returns d-1 dimensional histogram of (estimated) mean value of axis
        NB this is very different from averaging over the axis!!!

def average(self, axis):
        """Returns d-1 dimensional histogram of (estimated) mean value of axis
        NB this is very different from averaging over the axis!!!
        """
        axis = self.get_axis_number(axis)
        avg_hist = np.ma.average(self.all_axis_bin_centers(axis),
                                 weights=self.histogram, axis=axis)
        if self.dimensions == 2:
            new_hist = Hist1d
        else:
            new_hist = Histdd
        return new_hist.from_histogram(histogram=avg_hist,
                                       bin_edges=itemgetter(*self.other_axes(axis))(self.bin_edges),
                                       axis_names=self.axis_names_without(axis))