Example creating a feather file from a row-major double vector

to_feather_ex.cc

#include <iostream>
#include <vector>

#include <arrow/api.h>
#include <arrow/filesystem/api.h>
#include <arrow/ipc/api.h>

arrow::Status RunMain(int argc, char **argv) {

  std::vector<std::vector<double>> rows = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};

  // Convert your row-vector to a vector of columns (arrow::Array)
  std::vector<arrow::DoubleBuilder> column_builders(rows.size());
  for (const auto &row : rows) {
    for (std::size_t col_idx = 0; col_idx < row.size(); col_idx++) {
      column_builders[col_idx].Append(row[col_idx]);
    }
  }
  std::vector<std::shared_ptr<arrow::Array>> columns;
  for (std::size_t col_idx = 0; col_idx < column_builders.size(); col_idx++) {
    ARROW_ASSIGN_OR_RAISE(auto col, column_builders[col_idx].Finish());
    columns.push_back(col);
  }

  // Create schema (insert field names here)
  std::vector<std::shared_ptr<arrow::Field>> fields;
  for (std::size_t col_idx = 0; col_idx < columns.size(); col_idx++) {
    fields.push_back(
        arrow::field("Field " + std::to_string(col_idx), arrow::float64()));
  }
  auto schema = arrow::schema(fields);

  // Create record batch
  auto record_batch = arrow::RecordBatch::Make(
      schema, static_cast<int64_t>(rows.size()), columns);

  // Open output file
  arrow::fs::LocalFileSystem fs;
  ARROW_ASSIGN_OR_RAISE(auto output_stream,
                        fs.OpenOutputStream("/tmp/foo.feather"));

  ARROW_ASSIGN_OR_RAISE(auto writer,
                        arrow::ipc::MakeFileWriter(output_stream, schema));

  ARROW_RETURN_NOT_OK(writer->WriteRecordBatch(*record_batch));

  return writer->Close();
}

int main(int argc, char **argv) {
  arrow::Status st = RunMain(argc, argv);
  if (!st.ok()) {
    std::cerr << st << std::endl;
    return 1;
  }
  return 0;
}