def unique(self, column: str) -> Dict[str, List]:
        """Return a list of the unique elements in a column for each split.

        This is implemented in the low-level backend and as such, very fast.

        Args:
            column (`str`):
                column name (list all the column names with [`~datasets.DatasetDict.column_names`])

        Returns:
            Dict[`str`, `list`]: Dictionary of unique elements in the given column.

        Example:

        ```py
        >>> from datasets import load_dataset
        >>> ds = load_dataset("rotten_tomatoes")
        >>> ds.unique("label")
        {'test': [1, 0], 'train': [1, 0], 'validation': [1, 0]}
        ```
        """
        self._check_values_type()
        return {k: dataset.unique(column) for k, dataset in self.items()}