def _undo_enumerate(_idx, row):
    """
    A :py:meth:`tf.data.Dataset.map` function for
    reversing the :py:meth:`tf.data.Dataset.enumerate()`
    transformation.

    This function takes a :py:class:`tf.data.Dataset`
    of shape ``(idx, row)`` and returns the ``row``.
    """
    return row