def METHOD_NAME(self) -> Dict[str, List[str]]:
    """
    Returns a dict mapping from each dataset category to a list of its
    sequence names.
    Returns:
        category_to_sequence_names: Dict {category_i: [..., sequence_name_j, ...]}
    """
    c2seq = defaultdict(list)
    for sequence_name in self.sequence_names():
        first_frame_idx = next(self.sequence_indices_in_order(sequence_name))
        # crashes without overriding __getitem__
        sequence_category = self[first_frame_idx].sequence_category
        c2seq[sequence_category].append(sequence_name)
    return dict(c2seq)