def _map_channels_to_measurement_lists(snirf):
    """Returns a map of measurementList index to measurementList group name."""
    prefix = "measurementList"
    data_keys = snirf["nirs"]["data1"].keys()
    mls = [k for k in data_keys if k.startswith(prefix)]

    def _extract_channel_id(ml):
        return int(ml[len(prefix) :])

    return {_extract_channel_id(ml): ml for ml in mls}