CalibrationStatisticsFlatMap statistics_map;
  for (const std::string& statistics_file : statistics_files) {
    TF_ASSIGN_OR_RETURN(
        const auto single_map,
        io::ReadBinaryProto<CalibrationStatisticsMap>(
            tsl::io::JoinPath(calibration_data_dir, statistics_file)));
    statistics_map.insert(single_map.statistics().begin(),
                          single_map.statistics().end());
  }