[Rcpp-devel] conditionally created vectors

[Hideyoshi Maeda]

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