presto-orc/src/main/java/io/prestosql/orc/StripeReader.java/StripeReader/getRowGroupStatistics
class StripeReader:    private static ColumnMetadata<ColumnStatistics> getRowGroupStatistics(ColumnMetadata<OrcType> types, Map<StreamId, List<RowGroupIndex>> columnIndexes, int rowGroup)
    {
        requireNonNull(columnIndexes, "columnIndexes is null");
        checkArgument(rowGroup >= 0, "rowGroup is negative");

        Map<Integer, List<RowGroupIndex>> rowGroupIndexesByColumn = columnIndexes.entrySet().stream()
                .collect(toImmutableMap(entry -> entry.getKey().getColumnId().getId(), Entry::getValue));

        List<ColumnStatistics> statistics = new ArrayList<>(types.size());
        for (int columnIndex = 0; columnIndex < types.size(); columnIndex++) {
            List<RowGroupIndex> rowGroupIndexes = rowGroupIndexesByColumn.get(columnIndex);
            if (rowGroupIndexes != null) {
                statistics.add(rowGroupIndexes.get(rowGroup).getColumnStatistics());
            }
            else {
                statistics.add(null);
            }
        }
        return new ColumnMetadata<>(statistics);
    }