Rcpp 中的二义性重载运算符

Question

This is a revised question

In r, and Rcpp I have a string declared as string def; I also have a data frame called Row_Labels that contains two-letter strings, "AA", "BB", etc. Now I am trying to do this..

#include <Rcpp.h>
#include <string.h>
//using namespace Rcpp;
//using namespace std;


// [[Rcpp::export]]
Rcpp::DataFrame process_Data(Rcpp::DataFrame df,Rcpp::DataFrame Row_Labels, Rcpp::DataFrame Column_Labels){

  Rcpp::Rcout << "Test value from 'cout' " << std::endl;
  Rcpp::Rcout << "Number of rows in df = " << df.nrow() << std::endl;

  std::string abc;
  abc = "test value";
  std::string def;
  def = "zz";

    for(int i = 0; i < Row_Labels.nrow() ; i++)
    {

      def = Row_Labels[i];  // error here

      Rcpp::Rcout << "Row_Labels = " << i;
      Rcpp::Rcout << i << " " << Row_Labels[i] << std::endl; // error here

   }


  return Rcpp::DataFrame::create(Rcpp::_["a"]= df);

}

I am getting an error that is... use of overload operator'=' is ambiguous (with operand types 'string' (aka 'based_string <char, char traits <char>, allocator <char> >') and 'Proxy' (aka 'generic proxy<19>'))

I appreciate the help and hope this revision is more helpful

Answer 1

You have a pretty simple error there: If row and column labels are of type DateFrame then you cannot index as you do in Row_Labels[i]; -- these are not vectors. Fix: use vectors instead. This also requires to use length() rather than nrow() . So the following compiles fine:

#include <Rcpp.h>

// [[Rcpp::export]]
Rcpp::DataFrame process_Data(Rcpp::DataFrame df,
                             Rcpp::CharacterVector Row_Labels,
                             Rcpp::CharacterVector Column_Labels){

  Rcpp::Rcout << "Test value from 'cout' " << std::endl;
  Rcpp::Rcout << "Number of rows in df = " << df.nrow() << std::endl;

  std::string abc = "test value";
  std::string def = "zz";

  for(int i = 0; i < Row_Labels.length() ; i++) {
      def = Row_Labels[i];  // error here
      Rcpp::Rcout << "Row_Labels = " << i;
      Rcpp::Rcout << i << " " << Row_Labels[i] << std::endl; // error here
  }
  return Rcpp::DataFrame::create(Rcpp::_["a"]= df);
}

I also tightened and shortend it a little.