Function ReadTableManually

cpp/src/parquet/arrow/arrow_reader_writer_test.cc:2515–2534

Exercise reading table manually with nested RowGroup and Column loops, i.e. for (int i = 0; i < n_row_groups; i++) for (int j = 0; j < n_cols; j++) reader->RowGroup(i)->Column(j)->Read(&chunked_array);

//    for (int j = 0; j < n_cols; j++)
//      reader->RowGroup(i)->Column(j)->Read(&chunked_array);
::arrow::Result<std::shared_ptr<Table>> ReadTableManually(FileReader* reader) {
  std::vector<std::shared_ptr<Table>> tables;

  std::shared_ptr<::arrow::Schema> schema;
  RETURN_NOT_OK(reader->GetSchema(&schema));

  int n_row_groups = reader->num_row_groups();
  int n_columns = schema->num_fields();
  for (int i = 0; i < n_row_groups; i++) {
    std::vector<std::shared_ptr<ChunkedArray>> columns{static_cast<size_t>(n_columns)};

    for (int j = 0; j < n_columns; j++) {
      RETURN_NOT_OK(reader->RowGroup(i)->Column(j)->Read(&columns[j]));
    }

    tables.push_back(Table::Make(schema, columns));
  }

  return ConcatenateTables(tables);
}

TEST(TestArrowReadWrite, ReadTableManually) {
  const int num_columns = 1;