code: def _get_values(self):
          
          (gi, _), (ci, _), (si, _) = self._get_dims(self.hmap.last)
          ndims = self.hmap.last.ndims
          dims = self.hmap.last.kdims
          dimensions = []
          values = {}
          for vidx, vtype in zip([gi, ci, si], self._dimensions):
              if vidx < ndims:
                  dim = dims[vidx]
                  dimensions.append(dim)
                  vals = self.hmap.dimension_values(dim.name)
              else:
                  dimensions.append(None)
                  vals = [None]
              values[vtype] = list(unique_iterator(vals))
          return values, dimensions
docs: Get unique index value for each bar