Get unique index value for each bar

def _get_values(self):
        """
        Get unique index value for each bar
        """
        (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