[Rcpp-devel] conditionally created vectors

wrote:

So I'm guessing there is no simple export outside of the {} function?
On 13 Feb 2014, at 18:17, Dirk Eddelbuettel <edd at debian.org> wrote:

On 13 February 2014 at 17:48, Hideyoshi Maeda wrote:
| Dear Rcpp-Devel list,
|
| I am relatively new to Rcpp and am struggling to work out why the

following code does not compile.

|
| #include <Rcpp.h>
| using namespace Rcpp;
|
| // [[Rcpp::export]]
| Rcpp::NumericVector f1(String typ){
|   if(typ=="nc"){
|     Rcpp::NumericVector xx(10);
|   } else {
|     Rcpp::NumericVector xx(20);
|   }
|   return xx;
| }

"Scope".

You create 'xx' inside the { } and it does not exist outside of those.

| Basically the function takes in a string input and if its has the

value "nc" then it returns a zero string of length 10 and if it doesn't
then it should return a zero vector of length 20. I don't quite understand
why the above code works but the below code does. What do I need to do to
make the above code work,  so that I can call xx after the if statement is
done?

|
| #include <Rcpp.h>
| using namespace Rcpp;
|
| // [[Rcpp::export]]
| Rcpp::NumericVector f1(String typ){
|   if(typ=="nc"){
|     Rcpp::NumericVector xx(10);
|     return xx;
|   } else {
|     Rcpp::NumericVector xx(20);
|     return xx;
|   }
| }

Try this. It uses RcppArmadillo which has a resize() member function.


// [[Rcpp::depends(RcppArmadillo)]]

#include <RcppArmadillo.h>


// [[Rcpp::export]]
arma::colvec f1(std::string typ){
 arma::colvec xx;
 if (typ=="nc"){
   xx.resize(10);
 } else {
   xx.resize(20);
 }
 return xx;
}

Dirk

--
Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com