[GitHub] [orc] coderex2522 commented on issue #1220: How to set list's offsets correctly

[GitBox <gi...@apache.org>]

coderex2522 commented on issue #1220:
URL: https://github.com/apache/orc/issues/1220#issuecomment-1220202314

   For List type, the length of the offset array is one greater than the number of rows. Because the number of elements in the current row is confirmed by offsets[row] - offsets[row - 1](row number>= 1). So your example code needs to add the following two lines.
   void write_orc()
   {
       using namespace orc;
   
       ORC_UNIQUE_PTR<OutputStream> outStream = writeLocalFile("test-file.orc");
       ORC_UNIQUE_PTR<Type> schema(
           Type::buildTypeFromString("struct<id:int,list1:array<string>>"));
       WriterOptions options;
       ORC_UNIQUE_PTR<Writer> writer = createWriter(*schema, outStream.get(), options);
   
       std::unique_ptr<Writer> writer = createWriter(*type, stream.get(), options);
   
       uint64_t batch_size = 1024, row_count = 2048;
   
       std::unique_ptr<ColumnVectorBatch> batch =
           writer->createRowBatch(row_count);
       StructVectorBatch &root_batch =
           dynamic_cast<StructVectorBatch &>(*batch.get());
       LongVectorBatch &id_batch =
           dynamic_cast<LongVectorBatch &>(*struct_batch.fields[0]);
       ListVectorBatch &list_batch =
           dynamic_cast<ListVectorBatch &>(*struct_batch.fields[1]);
       StringVectorBatch &str_batch =
           dynamic_cast<StringVectorBatch &>(*list_batch.elements.get());
       
       std::vector<std::string> vs{"str1", "str2"};
   
       char **data         = str_batch.data.data();
       int64_t *offsets    = list_batch.offsets.data();
       uint64_t offset     = 0, rows = 0;
       for (size_t i = 0; i < row_count; ++i) {
           offsets[rows] = static_cast<int64_t>(offset);
   
           id_batch.data[rows] = articles[i]->get_id();
   
           for (auto &s : vs)
           {
               data[offset] = &s[0];
               str_batch.length[offset++] = s.size();
           }
   
           rows++;
           if (rows == batch_size) 
           {
               offsets[rows] = offset; // new line
               root_batch.numElements = rows;
               id_batch.numElements   = rows;
               list_batch.numElements = rows;
   
               writer->add(*batch);
               rows = 0;
               offset = 0;
           }
       }
   
       if (rows != 0) 
       {
           offsets[rows] = offset; // new line
           root_batch.numElements = rows;
           id_batch.numElements   = rows;
           list_batch.numElements = rows;
   
           writer->add(*batch);
           rows = 0;
           offset = 0;
       }
   
       writer->close();
   }


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