@contextlib.contextmanager
    def formatted_as(
        self,
        type: Optional[str] = None,
        columns: Optional[List] = None,
        output_all_columns: bool = False,
        **format_kwargs,
    ):
        """To be used in a `with` statement. Set `__getitem__` return format (type and columns).
        The transformation is applied to all the datasets of the dataset dictionary.