in src/main/java/com/google/cloud/solutions/autotokenize/common/SortCsvRow.java [188:196]
public static CsvRowToSortNameKV usingColumnNames(List<String> orderingColumns) {
checkNotNull(orderingColumns);
checkArgument(orderingColumns.size() > 0 && orderingColumns.size() <= 2);
var primaryKey = orderingColumns.get(0);
var secondaryKey = (orderingColumns.size() == 2) ? orderingColumns.get(1) : null;
return create(primaryKey, secondaryKey);
}