Function MakeSimpleArray

r/src/r_to_arrow.cpp:1229–1273

// the R object, via an RBuffer, hence be zero copy
template <int RTYPE, typename RVector, typename Type>
std::shared_ptr<Array> MakeSimpleArray(SEXP x) {
  using value_type = typename arrow::TypeTraits<Type>::ArrayType::value_type;
  RVector vec(x);
  auto n = vec.size();
  auto p_vec_start = reinterpret_cast<const value_type*>(DATAPTR_RO(vec));
  auto p_vec_end = p_vec_start + n;
  std::vector<std::shared_ptr<Buffer>> buffers{nullptr,
                                               std::make_shared<RBuffer<RVector>>(vec)};

  int null_count = 0;

  auto first_na = std::find_if(p_vec_start, p_vec_end, is_NA<value_type>);
  if (first_na < p_vec_end) {
    auto null_bitmap =
        ValueOrStop(AllocateBuffer(bit_util::BytesForBits(n), gc_memory_pool()));
    internal::FirstTimeBitmapWriter bitmap_writer(null_bitmap->mutable_data(), 0, n);

    // first loop to clear all the bits before the first NA
    auto j = std::distance(p_vec_start, first_na);
    int i = 0;
    for (; i < j; i++, bitmap_writer.Next()) {
      bitmap_writer.Set();
    }

    auto p_vec = first_na;
    // then finish
    for (; i < n; i++, bitmap_writer.Next(), ++p_vec) {
      if (is_NA<value_type>(*p_vec)) {
        bitmap_writer.Clear();
        null_count++;
      } else {
        bitmap_writer.Set();
      }
    }

    bitmap_writer.Finish();
    buffers[0] = std::move(null_bitmap);
  }

  auto data = ArrayData::Make(std::make_shared<Type>(), LENGTH(x), std::move(buffers),
                              null_count, 0 /*offset*/);

  // return the right Array class
  return std::make_shared<typename TypeTraits<Type>::ArrayType>(data);
}

std::shared_ptr<arrow::Array> vec_to_arrow__reuse_memory(SEXP x) {
  auto type = TYPEOF(x);