I will be grateful for any hint on how to correct the code. I am a beginner with the Rccp package and R programming. I have an R data frame df with special columns (columns with lists), to simulate my processed gene expression data:

df<- data.frame(w= 1:3, x=3:5, y=6:8, z = I(list(1:2, 1:3, 1:4)))
df <- as.data.frame(do.call(cbind, lapply(df[1:3], function(x) Map("*", df$z, x))))

>df

           w                x                  y
        1, 2             3, 6              6, 12
     2, 4, 6         4, 8, 12          7, 14, 21
3, 6, 9, 12    5, 10, 15, 20      8, 16, 24, 32

My goal is to have a data frame df1 by interfacing C++ and R in order to speed up my code, while preserving the data frame structure.

df1 <- as.data.frame (4*sin(df*pi))

I have attempted :

library(Rcpp)
cppFunction('NumericVector transfo(Rcpp::DataFrame x) {
  int nrow = x.nrow(), ncol = x.ncol();
           NumericVector out(nrow*ncol);
           int pi;
           int vol = 4;
           for (int j = 0; j < ncol; j++) {
           for (int i = 0; i < nrow; i++) {
           out[i, j] = sin(x[i,j]*pi)*vol;
           }
           }
           return out;
           }')

But with transfo(df): I get the error :

Expecting a single value: [extent=3]

I will be grateful for any hint on how to make the code work.