Why do I get the error for using “pnorm” in Rcpp

Question

I need to involve variable from arma::in my Rcpp code. But I ran into a problem when trying to use the sugar function pnorm. Here is a demo:

Answer 1

I'm much less of an expert than @RalfStubner at Rcpp, so I had to hack around (with help from StackOverflow and the Rcpp cheat sheat) to get the following code. Instead of using the R-namespace versions on scalars, I converted back to a NumericVector ... this can almost certainly be done more efficiently/skipping a few steps by someone who actually knows what they're doing ... e.g. it's possible that the arma-to-NumericVector conversion could be done directly without going through as_scalar ... ?

#include <RcppArmadillo.h>
#include <RcppArmadilloExtensions/sample.h>
#include <Rcpp.h>

// [[Rcpp::depends(RcppArmadillo)]]
using namespace Rcpp;
using namespace arma;

// [[Rcpp::export]]
NumericVector pget(NumericVector x, NumericVector beta) {
  colvec xx = as<colvec>(x) ;
  colvec bb = as<colvec>(beta) ;
  double tt = as_scalar(trans(xx) * bb);
  NumericVector tt2 = NumericVector::create( tt );
  NumericVector temp = Rcpp::pnorm(tt2);
  return temp;
}

Answer 2

The Rcpp sugar functions are meant for vector type arguments like Rcpp::NumericVector. For scalar arguments you can use the functions in the R namespace:

#include <RcppArmadillo.h>
#include <RcppArmadilloExtensions/sample.h>
// [[Rcpp::depends(RcppArmadillo)]]
using namespace Rcpp;

// [[Rcpp::export]]
double pget(NumericVector x, NumericVector beta) {
  arma::colvec xx = Rcpp::as<arma::colvec>(x) ;
  arma::colvec bb = Rcpp::as<arma::colvec>(beta) ;
  double tt = as_scalar( arma::trans(xx) * bb);
  double temp = R::pnorm(tt, 0.0, 1.0, 1, 0);
  return temp;
}

/*** R
x <- rnorm(5)
beta <- rnorm(5)
pget(x, beta)
*/

BTW, here two variants. First variant uses arma instead of Rcpp vectors as arguments. Since these are const references, no data is copied. In addition, arma::dot is used:

// [[Rcpp::export]]
double pget2(const arma::colvec& xx, const arma::colvec& bb) {
  double tt = arma::dot(xx, bb);
  return R::pnorm(tt, 0.0, 1.0, 1, 0);
}

The second variant calculates the scalar product without resorting to Armadillo:

// [[Rcpp::export]]
double pget3(NumericVector x, NumericVector beta) {
  double tt = Rcpp::sum(x * beta);
  return R::pnorm(tt, 0.0, 1.0, 1, 0);
}