Rcpp lapply() or mapply() with 5 arguments

Question

I have two functions that are conceptually like the two below. The first one builds a model with a set of parameters. The second one builds all models with 4 parameters held constant and one supplied in a list.

build_one_model <- function(a, b, x, c, d) {
  a + b + x + c + d
}
build_all_models <- function(a, b, xList, c, d) {
  lapply(xList, function(x) build_one_model(a, b, x, c, d))
}

Example usage:

xList <- list(1, 2, 3)
build_all_models(1, 2, xList, 4, 5)

[[1]]
[1] 13

[[2]]
[1] 14

[[3]]
[1] 15

Now I can convert build_one_model() to Rcpp:

#include <Rcpp.h>
using namespace Rcpp;

//[[Rcpp::export]]
double build_one_model(double a, double b, double x, double c, double d) {
  return a + b + x + c + d;
}

But how can I convert build_all_models()? lapply() only takes one input, and mapply() takes up to three, but I have 5.

Answer 1

I think I can settle with a for loop. I have to remind myself that I'm in C++ and not R, so for loops are not bad.

#include <Rcpp.h>
using namespace Rcpp;

//[[Rcpp::export]]
double build_one_model(double a, double b, double x, double c, double d) {
  return a + b + x + c + d;
}

//[[Rcpp::export]]
List build_all_models(double a, double b, List xList, double c, double d) {

  Rcpp::List ans(xList.length());
  for (int i = 0; i < xList.length(); i++) {
    ans[i] = build_one_model(a, b, xList[i], c, d);  
  }
  return ans;
}

xList <- list(1, 2, 3)
build_all_models(1, 2, xList, 4, 5)

[[1]]
[1] 13

[[2]]
[1] 14

[[3]]
[1] 15