template map to list conversion

Author: pachadotdev

cpp11test/R/cpp11.R

@@ -92,6 +92,10 @@ ordered_map_to_list_ <- function(x) {
   .Call(`_cpp11test_ordered_map_to_list_`, x)
 }
 
+ordered_map_to_list_2_ <- function(x) {
+  .Call(`_cpp11test_ordered_map_to_list_2_`, x)
+}
+
 unordered_map_to_list_ <- function(x) {
   .Call(`_cpp11test_unordered_map_to_list_`, x)
 }

cpp11test/src/cpp11.cpp

@@ -181,6 +181,13 @@ extern "C" SEXP _cpp11test_ordered_map_to_list_(SEXP x) {
   END_CPP11
 }
 // map.cpp
+SEXP ordered_map_to_list_2_(cpp11::doubles x);
+extern "C" SEXP _cpp11test_ordered_map_to_list_2_(SEXP x) {
+  BEGIN_CPP11
+    return cpp11::as_sexp(ordered_map_to_list_2_(cpp11::as_cpp<cpp11::decay_t<cpp11::doubles>>(x)));
+  END_CPP11
+}
+// map.cpp
 SEXP unordered_map_to_list_(cpp11::doubles x);
 extern "C" SEXP _cpp11test_unordered_map_to_list_(SEXP x) {
   BEGIN_CPP11
@@ -515,6 +522,7 @@ static const R_CallMethodDef CallEntries[] = {
     {"_cpp11test_my_warning_n1fmt",         (DL_FUNC) &_cpp11test_my_warning_n1fmt,         1},
     {"_cpp11test_my_warning_n2fmt",         (DL_FUNC) &_cpp11test_my_warning_n2fmt,         2},
     {"_cpp11test_ordered_map_to_list_",     (DL_FUNC) &_cpp11test_ordered_map_to_list_,     1},
+    {"_cpp11test_ordered_map_to_list_2_",   (DL_FUNC) &_cpp11test_ordered_map_to_list_2_,   1},
     {"_cpp11test_protect_many_",            (DL_FUNC) &_cpp11test_protect_many_,            1},
     {"_cpp11test_protect_many_cpp11_",      (DL_FUNC) &_cpp11test_protect_many_cpp11_,      1},
     {"_cpp11test_protect_many_preserve_",   (DL_FUNC) &_cpp11test_protect_many_preserve_,   1},

cpp11test/src/map.cpp

@@ -10,6 +10,15 @@
   return cpp11::as_sexp(counts);
 }
 
+[[cpp11::register]] SEXP ordered_map_to_list_2_(cpp11::doubles x) {
+  std::map<double, double> counts;
+  double n = x.size();
+  for (int i = 0; i < n; i++) {
+    counts[x[i]] += 1.0;
+  }
+  return cpp11::as_sexp(counts);
+}
+
 [[cpp11::register]] SEXP unordered_map_to_list_(cpp11::doubles x) {
   std::unordered_map<double, int> counts;
   int n = x.size();

cpp11test/tests/testthat/test-map-to-list.R

@@ -6,6 +6,9 @@ test_that("ordered and unordered C++ maps are converted to R lists", {
   om <- ordered_map_to_list_(x)
   expect_type(om, "list")
 
+  om2 <- ordered_map_to_list_2_(x)
+  expect_equal(om, om2)
+
   om_doubles <- as.double(names(om))
   expect_equal(om_doubles, sort(om_doubles))
 

inst/include/cpp11/as.hpp

@@ -336,33 +336,18 @@ enable_if_convertible_to_sexp<T, SEXP> as_sexp(const T& from) {
   return from;
 }
 
-// Pacha: Specialization for std::map
-// NOTE: I did not use templates to avoid clashes with doubles/function/etc.
-inline SEXP as_sexp(const std::map<std::string, SEXP>& map) {
-  R_xlen_t size = map.size();
-  SEXP result = PROTECT(Rf_allocVector(VECSXP, size));
-  SEXP names = PROTECT(Rf_allocVector(STRSXP, size));
-
-  auto it = map.begin();
-  for (R_xlen_t i = 0; i < size; ++i, ++it) {
-    SET_VECTOR_ELT(result, i, it->second);
-    SET_STRING_ELT(names, i, Rf_mkCharCE(it->first.c_str(), CE_UTF8));
-  }
-
-  Rf_setAttrib(result, R_NamesSymbol, names);
-  UNPROTECT(2);
-  return result;
-}
-
-// Specialization for std::map<double, int>
-inline SEXP as_sexp(const std::map<double, int>& map) {
+// Templated specialization for std::map
+template <typename Key, typename Value,
+          typename = enable_if_t<std::is_arithmetic<Key>::value &&
+                                 std::is_arithmetic<Value>::value>>
+inline SEXP as_sexp(const std::map<Key, Value>& map) {
   R_xlen_t size = map.size();
   SEXP result = PROTECT(Rf_allocVector(VECSXP, size));
   SEXP names = PROTECT(Rf_allocVector(REALSXP, size));
 
   auto it = map.begin();
   for (R_xlen_t i = 0; i < size; ++i, ++it) {
-    SET_VECTOR_ELT(result, i, Rf_ScalarInteger(it->second));
+    SET_VECTOR_ELT(result, i, as_sexp(it->second));
     REAL(names)[i] = it->first;
   }
 
@@ -371,32 +356,18 @@ inline SEXP as_sexp(const std::map<double, int>& map) {
   return result;
 }
 
-// Pacha: Specialization for std::unordered_map
-inline SEXP as_sexp(const std::unordered_map<std::string, SEXP>& map) {
-  R_xlen_t size = map.size();
-  SEXP result = PROTECT(Rf_allocVector(VECSXP, size));
-  SEXP names = PROTECT(Rf_allocVector(STRSXP, size));
-
-  auto it = map.begin();
-  for (R_xlen_t i = 0; i < size; ++i, ++it) {
-    SET_VECTOR_ELT(result, i, it->second);
-    SET_STRING_ELT(names, i, Rf_mkCharCE(it->first.c_str(), CE_UTF8));
-  }
-
-  Rf_setAttrib(result, R_NamesSymbol, names);
-  UNPROTECT(2);
-  return result;
-}
-
-// Specialization for std::unordered_map<double, int>
-inline SEXP as_sexp(const std::unordered_map<double, int>& map) {
+// Templated specialization for std::unordered_map
+template <typename Key, typename Value,
+          typename = enable_if_t<std::is_arithmetic<Key>::value &&
+                                 std::is_arithmetic<Value>::value>>
+inline SEXP as_sexp(const std::unordered_map<Key, Value>& map) {
   R_xlen_t size = map.size();
   SEXP result = PROTECT(Rf_allocVector(VECSXP, size));
   SEXP names = PROTECT(Rf_allocVector(REALSXP, size));
 
   auto it = map.begin();
   for (R_xlen_t i = 0; i < size; ++i, ++it) {
-    SET_VECTOR_ELT(result, i, Rf_ScalarInteger(it->second));
+    SET_VECTOR_ELT(result, i, as_sexp(it->second));
     REAL(names)[i] = it->first;
   }