第一次尝试在 Rcpp 中使用 R 函数时出错

Question

尝试在 Rcpp 中编译一个函数，该函数引入了一个名为 read_excel 的 R 包。

不确定错误是什么意思，但可能找不到包中的函数？

cppFunction('IntegerVector readYear(CharacterVector filePath ) {

 IntegerVector Year(filePath.size());
 int n=filePath.size();

 Environment pkg = Environment::namespace_env("readxl");

 Function read_excel=pkg["read_excel"];

 for( int i =0 ; i<n; i++){


 Year[i] = read_excel(Named("path") = filePath[i],
          _["range"] = "B3:B3",
          _["col_names"] = false );
 }
 return Year;
}')

错误信息：

file391220cd2e2.cpp: In function ‘Rcpp::IntegerVector readYear(Rcpp::CharacterVector)’:
file391220cd2e2.cpp:18:22: error: invalid conversion from ‘SEXP {aka SEXPREC*}’ to ‘Rcpp::traits::storage_type<13>::type {aka int}’ [-fpermissive]
  Year[i] = read_excel(Named("path") = filePath[i],
                      ^
make: *** [file391220cd2e2.o] Error 1
g++ -std=gnu++11 -I"/opt/R/3.6.0/lib/R/include" -DNDEBUG   -I"/home/rstudio-user/R/x86_64-pc-linux-gnu-library/3.6/Rcpp/include" -I"/tmp/RtmpbaxzNs/sourceCpp-x86_64-pc-linux-gnu-1.0.2" -I/usr/local/include  -fpic  -g -O2  -c file391220cd2e2.cpp -o file391220cd2e2.o
/opt/R/3.6.0/lib/R/etc/Makeconf:176: recipe for target 'file391220cd2e2.o' failed
Error in sourceCpp(code = code, env = env, rebuild = rebuild, cacheDir = cacheDir,  : 
  Error 1 occurred building shared library.

Answer 1

该错误消息表示无法直接将 R 函数的 return 类型（SEXP）转换为 IntegerVector 的存储类型（int).您可以使用 Rcpp::as<int>(...):

指示 Rcpp 这样做

Rcpp::cppFunction('IntegerVector readYear(CharacterVector filePath ) {

 int n = filePath.size();
 IntegerVector Year(n);

 Environment pkg = Environment::namespace_env("readxl");

 Function read_excel=pkg["read_excel"];

 for(int i =0; i<n; ++i){
   Year[i] = Rcpp::as<int>(read_excel(_("path") = filePath[i],
                                      _["range"] = "B3:B3",
                                      _["col_names"] = false ));
 }
 return Year;
}')

顺便说一句，我希望在 C++ 中这样做有充分的理由，因为它实际上比等效的 R 函数慢，因为从 C++ 调用 R 函数是有代价的。

第一次尝试在 Rcpp 中使用 R 函数时出错

Have error in trying to use R function in Rcpp for the first time

rcpp