presto-orc/src/main/java/io/prestosql/orc/OrcWriteValidation.java/OrcWriteValidation/buildActualRowGroupStatistics
class OrcWriteValidation:    private static RowGroupStatistics buildActualRowGroupStatistics(int rowGroupIndex, Map<StreamId, List<RowGroupIndex>> actualRowGroupStatistics)
    {
        return new RowGroupStatistics(
                BOTH,
                actualRowGroupStatistics.entrySet()
                        .stream()
                        .collect(Collectors.toMap(entry -> entry.getKey().getColumnId(), entry -> entry.getValue().get(rowGroupIndex).getColumnStatistics())));
    }