romainfrancois commented on a change in pull request #9615:
URL: https://github.com/apache/arrow/pull/9615#discussion_r628202179
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File path: r/src/r_to_arrow.cpp
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@@ -168,46 +207,85 @@ bool is_NA<int64_t>(int64_t value) {
}
template <typename T>
-struct RVectorVisitor {
+class RVectorIterator {
+ public:
+ using value_type = T;
+ RVectorIterator(SEXP x, int64_t start)
+ : ptr_x_(reinterpret_cast<const T*>(DATAPTR_RO(x)) + start) {}
+
+ RVectorIterator& operator++() {
+ ++ptr_x_;
+ return *this;
+ }
+
+ const T operator*() const { return *ptr_x_; }
+
+ private:
+ const T* ptr_x_;
+};
+
+template <typename T>
+class RVectorIterator_ALTREP {
+ public:
+ using value_type = T;
using data_type =
typename std::conditional<std::is_same<T, int64_t>::value, double,
T>::type;
using r_vector_type = cpp11::r_vector<data_type>;
+ using r_vector_iterator = typename r_vector_type::const_iterator;
- template <typename AppendNull, typename AppendValue>
- static Status Visit(SEXP x, int64_t size, AppendNull&& append_null,
- AppendValue&& append_value) {
- r_vector_type values(x);
- auto it = values.begin();
-
- for (R_xlen_t i = 0; i < size; i++, ++it) {
- auto value = GetValue(*it);
-
- if (is_NA<T>(value)) {
- RETURN_NOT_OK(append_null());
- } else {
- RETURN_NOT_OK(append_value(value));
- }
- }
+ RVectorIterator_ALTREP(SEXP x, int64_t start)
+ : vector_(x), it_(vector_.begin() + start) {}
- return Status::OK();
+ RVectorIterator_ALTREP& operator++() {
+ ++it_;
+ return *this;
}
+ const T operator*() const { return GetValue(*it_); }
+
static T GetValue(data_type x) { return x; }
+
+ private:
+ r_vector_type vector_;
+ r_vector_iterator it_;
};
template <>
-int64_t RVectorVisitor<int64_t>::GetValue(double x) {
+int64_t RVectorIterator_ALTREP<int64_t>::GetValue(double x) {
int64_t value;
memcpy(&value, &x, sizeof(int64_t));
return value;
}
+template <typename Iterator, typename AppendNull, typename AppendValue>
+Status VisitVector(Iterator it, int64_t n, AppendNull&& append_null,
+ AppendValue&& append_value) {
+ for (R_xlen_t i = 0; i < n; i++, ++it) {
Review comment:
We might revisit when we tackle chunking, iterator equality and `end()`
should be straightforward as the iterator classes we use are just wrappers
around either pointers or cpp11 iterators.
The only thing is that when we'll chunk, we might not iterate from start to
end.
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