Method Elt

r/src/altrep.cpp:861–887

Get a single string as a CHARSXP SEXP

  // Get a single string as a CHARSXP SEXP
  static SEXP Elt(SEXP alt, R_xlen_t i) {
    if (Base::IsMaterialized(alt)) {
      return STRING_ELT(Representation(alt), i);
    }

    auto altrep_data =
        reinterpret_cast<ArrowAltrepData*>(R_ExternalPtrAddr(R_altrep_data1(alt)));
    auto resolve = altrep_data->locate(i);
    const auto& array =
        altrep_data->chunked_array()->chunk(static_cast<int>(resolve.chunk_index));
    auto j = resolve.index_in_chunk;

    SEXP s = NA_STRING;
    RStringViewer& r_string_viewer = string_viewer();
    r_string_viewer.SetArray(array);
    // Note: we don't check GetBoolOption("arrow.skip_nul", false) here
    // because it is too expensive to do so. We do set this value whenever
    // an altrep string; however, there is a chance that this value could
    // be out of date by the time a value in the vector is accessed.
    r_string_viewer.reset_null_was_stripped();
    s = r_string_viewer.Convert(j);
    if (r_string_viewer.nul_was_stripped()) {
      Rf_warning("Stripping '\\0' (nul) from character vector");
    }

    return s;
  }

  static void* Dataptr(SEXP alt, Rboolean writeable) {
    return const_cast<void*>(DATAPTR_RO(Materialize(alt)));