Ytukyg

http://gallery.rcpp.org/articles/working-with-Rcpp-StringVector/

I used the above link to try because I want to work with a string or character vector in R

however Rcpp is for some reason concatenating the elements of the vector I am using Rcout to try to understand what is happening but I have no idea what it is:

cppFunction('CharacterVector test(NumericMatrix h, NumericMatrix nt, StringVector d, int r){



            CharacterVector m(h.ncol());

            Function f("paste0");

            for(int i = 0; i < d.size(); i++){

              Rcout << d[i];

            }



            return m;

            }')



h <- matrix(0,nrow=2, ncol =2)

colnames(h) <- c("A", "B")

nt <- matrix(0,nrow=2, ncol =2)



d <- c("2019-03", "2014-04")

test(h, nt, d, 1)

the output of Rcout is:

2019-032014-04[1] "" ""

in stead of:

"2019-03" "2014-04"

Why is this happening ?

If you want a space after each element you send to Rcpp::Rcout, you have to tell it so. You need to change

Rcout << d[i];

to

Rcout << d[i] << " ";

Also, as I now notice thanks to hrbrmstr's comment, you also want quotation marks around each element when they're printed. Again, if you want quotation marks, you have to tell that to Rcout, it doesn't happen automatically. Then, you'd further modify the aforementioned line to

Rcout << """ << d[i] << "" ";

I would also add a new line before the function ends. So, let's compare; I have my C++ code in the file so-answer.cpp:

#include <Rcpp.h>



using namespace Rcpp;



// [[Rcpp::export]]

CharacterVector test(NumericMatrix h, NumericMatrix nt, StringVector d, int r){



    CharacterVector m(h.ncol());

    Function f("paste0");

    for(int i = 0; i < d.size(); i++){

        Rcout << d[i];

    }



    return m;

}



// [[Rcpp::export]]

CharacterVector test2(NumericMatrix h, NumericMatrix nt, StringVector d, int r){



    CharacterVector m(h.ncol());

    Function f("paste0");

    for(int i = 0; i < d.size(); i++){

        Rcout << """ << d[i] << "" ";

    }



    Rcout << "n";



    return m;

}



/*** R

h <- matrix(0,nrow=2, ncol =2)

colnames(h) <- c("A", "B")

nt <- matrix(0,nrow=2, ncol =2)



d <- c("2019-03", "2014-04")

test(h, nt, d, 1)

test2(h, nt, d, 1)

*/

Then when I use Rcpp::sourceCpp() to compile and expose to R:

Rcpp::sourceCpp("so-answer.cpp")

#> 

#> > h <- matrix(0,nrow=2, ncol =2)

#> 

#> > colnames(h) <- c("A", "B")

#> 

#> > nt <- matrix(0,nrow=2, ncol =2)

#> 

#> > d <- c("2019-03", "2014-04")

#> 

#> > test(h, nt, d, 1)

#> 2019-032014-04[1] "" ""

#> 

#> > test2(h, nt, d, 1)

#> "2019-03" "2014-04" 

#> [1] "" ""

^{Created on 2018-11-23 by the reprex package (v0.2.1)}

I'll also note that I'm note sure what all the superfluous code is there for, but I just left it in.