From 279bc78a79f6220e3d87ada89edb0fdcfe9d204b Mon Sep 17 00:00:00 2001
From: Romain Francois <romain@rstudio.com>
Date: Wed, 8 Dec 2021 14:27:57 +0100
Subject: [PATCH 1/2] RPrimitiveConverter<duration>::Extend()

---
 r/src/r_to_arrow.cpp | 65 +++++++++++++++++++++++++++++++++-----------
 1 file changed, 49 insertions(+), 16 deletions(-)

diff --git a/r/src/r_to_arrow.cpp b/r/src/r_to_arrow.cpp
index 489cab80f60..8fd224836b3 100644
--- a/r/src/r_to_arrow.cpp
+++ b/r/src/r_to_arrow.cpp
@@ -583,6 +583,23 @@ int64_t get_TimeUnit_multiplier(TimeUnit::type unit) {
   }
 }
 
+Result<int> get_difftime_unit_multiplier(SEXP x) {
+  std::string unit(CHAR(STRING_ELT(Rf_getAttrib(x, symbols::units), 0)));
+  if (unit == "secs") {
+    return 1;
+  } else if (unit == "mins") {
+    return 60;
+  } else if (unit == "hours") {
+    return 3600;
+  } else if (unit == "days") {
+    return 86400;
+  } else if (unit == "weeks") {
+    return 604800;
+  } else {
+    return Status::Invalid("unknown difftime unit");
+  }
+}
+
 template <typename T>
 class RPrimitiveConverter<T, enable_if_t<is_time_type<T>::value>>
     : public PrimitiveConverter<T, RConverter> {
@@ -595,21 +612,7 @@ class RPrimitiveConverter<T, enable_if_t<is_time_type<T>::value>>
     }
 
     // multiplier to get the number of seconds from the value stored in the R vector
-    int difftime_multiplier;
-    std::string unit(CHAR(STRING_ELT(Rf_getAttrib(x, symbols::units), 0)));
-    if (unit == "secs") {
-      difftime_multiplier = 1;
-    } else if (unit == "mins") {
-      difftime_multiplier = 60;
-    } else if (unit == "hours") {
-      difftime_multiplier = 3600;
-    } else if (unit == "days") {
-      difftime_multiplier = 86400;
-    } else if (unit == "weeks") {
-      difftime_multiplier = 604800;
-    } else {
-      return Status::Invalid("unknown difftime unit");
-    }
+    ARROW_ASSIGN_OR_RAISE(int difftime_multiplier, get_difftime_unit_multiplier(x));
 
     // then multiply the seconds by this to match the time unit
     auto multiplier =
@@ -825,7 +828,37 @@ class RPrimitiveConverter<T, enable_if_t<is_duration_type<T>::value>>
     : public PrimitiveConverter<T, RConverter> {
  public:
   Status Extend(SEXP x, int64_t size, int64_t offset = 0) override {
-    // TODO: look in lubridate
+    auto rtype = GetVectorType(x);
+
+    // only handle <difftime> R objects
+    if (rtype == DURATION) {
+      RETURN_NOT_OK(this->Reserve(size - offset));
+
+      ARROW_ASSIGN_OR_RAISE(int difftime_multiplier, get_difftime_unit_multiplier(x));
+
+      int64_t multiplier = get_TimeUnit_multiplier(this->primitive_type_->unit()) * difftime_multiplier;
+
+      auto append_value = [this, multiplier](double value) {
+        auto converted = static_cast<typename T::c_type>(value * multiplier);
+        this->primitive_builder_->UnsafeAppend(converted);
+        return Status::OK();
+      };
+      auto append_null = [this]() {
+        this->primitive_builder_->UnsafeAppendNull();
+        return Status::OK();
+      };
+
+      if (ALTREP(x)) {
+        return VisitVector(RVectorIterator_ALTREP<double>(x, offset), size, append_null,
+                           append_value);
+      } else {
+        return VisitVector(RVectorIterator<double>(x, offset), size, append_null,
+                           append_value);
+      }
+
+      return Status::OK();
+    }
+
     return Status::NotImplemented("Extend");
   }
 };

From bcb1ce9ca0d8a7792e4d61f4e35f1d6fd7967955 Mon Sep 17 00:00:00 2001
From: Romain Francois <romain@rstudio.com>
Date: Fri, 10 Dec 2021 11:20:12 +0100
Subject: [PATCH 2/2] comment

---
 r/src/r_to_arrow.cpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/r/src/r_to_arrow.cpp b/r/src/r_to_arrow.cpp
index 8fd224836b3..51483cdf861 100644
--- a/r/src/r_to_arrow.cpp
+++ b/r/src/r_to_arrow.cpp
@@ -607,6 +607,7 @@ class RPrimitiveConverter<T, enable_if_t<is_time_type<T>::value>>
   Status Extend(SEXP x, int64_t size, int64_t offset = 0) override {
     RETURN_NOT_OK(this->Reserve(size - offset));
     auto rtype = GetVectorType(x);
+    // This probably also not accept duration
     if (rtype != TIME && rtype != DURATION) {
       return Status::Invalid("Invalid conversion to time");
     }