jonlachmann / rcpp.package

Demo rcpp package

rcpp.package

An R package that just contains a single Rcpp function doing addition of two numbers. The idea is to use this as a base for learning how to create R packages with functions implemented in C++ using Rcpp.

Usage

• Clone the git repository (using git clone or just download the repo on github).
• Open the folder using RStudio or PyCharm and run Rcpp::compileAttributes().
  • This generates the needed files R/RcppExports.R and src/RcppExports.cpp
  • Other files are also generated, namely addition.o, rcpp.package.so and RcppExports.o. These are specific to the system where the package is built (i.e. OSX, Windows, Linux) and should not be included in the code that is saved on e.g. github.
• To build and install the package, simply run pack <- devtools::build(); install.packages(pack).
• You can now load the package in R using library(rcpp.package). This also exposes the example function addition(a, b) which simply adds two numbers and returns the result.

Adding Rcpp functions

• Rcpp functions are stored in .cpp files in the src folder. Create a new file in that folder, making sure the file ending is .cpp.
• Begin the file with the following lines

#include <Rcpp.h>
using namespace Rcpp;

// [[Rcpp::export]]
return_type my_function(argument_1_type argument_1) {
  // Your code here
}

• An explanation of what we see in the code above:
  • The first line adds the necessary header file Rcpp.h so we can use Rcpp functions in our C++ code.
  • The second line is optional, it lets us use functions from Rcpp without writing Rcpp::Rcpp_function().
  • C++ comments are marked with //, writing // [[Rcpp::export]] lets devtools know that it should expose the function below to be used from R.
  • Finally we have the function body. Note C++ is a strongly typed language, meaning that every variable must be preceded by the type it has.
• When you are happy with your function, run devtools::document() to generate the files R/RcppExports.R and src/RcppExports.cpp.
• DO NOT edit the RcppExports files manually, it is just unneccesary work.