[Rcpp-devel] conditionally created vectors
Dirk Eddelbuettel
edd at debian.org
Thu Feb 13 19:17:24 CET 2014
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
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