Sums all data along all other axes, then return Hist1D

def projection(self, axis):
        """Sums all data along all other axes, then return Hist1D"""
        axis = self.get_axis_number(axis)
        projected_hist = np.sum(self.histogram, axis=self.other_axes(axis))
        return Hist1d.from_histogram(projected_hist, bin_edges=self.bin_edges[axis])