Rcpp: Excpecting Single Value

[EWeiss]

I've got two files: main.R and mv.cpp.

main.R:

main.R

library(Rcpp)

r <- data.frame(replicate(10, sample(0:10, 10000, replace = TRUE)))

mv(r)

and mv.cpp

#include <Rcpp.h>
using namespace Rcpp;

// [[Rcpp::export]]
void mv(Rcpp::DataFrame x){
int n = 0;
int nrow = x.nrow();
int ncol = x.ncol();
int mv = 0;

  for (int t =0; t < 10 + 0*nrow; t++){
     mv = x[0, t];
     for (int d = 0; d < ncol; d++){
           if (NumericVector::is_na(x[d,t])){
             x[d,t ] = mv;
             n++;
          } else {
               mv = x[d, t];
          }
       }
  }
  return;

}

I compile mv.cpp and then run main.R and get the error message:
Error in mv(r) : Expecting a single value: [extent=10000].

I've tried changing mv.cpp from void to int and still get the same error.

[nirgrahamuk]

you aren't returning any expression. did you intend to return the mv that you calculate within the loop ?

[EWeiss]

I want to replace missing values with the previous valid value. Each column is a variable and each row is a sequential observation. I made it "void mv()" to make it as simple as possible and to isolate the problem.
Thanks for your interest.