def _group_samples_by_protocol():
name_by_protocol = defaultdict(list)<EOL>for sn, p in PROTOCOL_BY_SAMPLE.items():<EOL><INDENT>name_by_protocol[p].append(sn)<EOL><DEDENT>return name_by_protocol<EOL>
Invert mapping from protocol name to sample name.

    :return Mapping[str, list[str]]: sample names by protocol name