code: def stack(cls, areas):
          
          if not len(areas):
              return areas
          baseline = np.zeros(len(areas.values()[0]))
          stacked = areas.clone(shared_data=False)
          vdims = [areas.values()[0].vdims[0], 'Baseline']
          for k, area in areas.items():
              x, y = (area.dimension_values(i) for i in range(2))
              stacked[k] = area.clone((x, y+baseline, baseline), vdims=vdims,
                                      new_type=Area)
              baseline = baseline + y
          return stacked
docs: Stacks an (Nd)Overlay of Area or Curve Elements by offsetting
          their baselines. To stack a HoloMap or DynamicMap use the map
          method.