R Packages

Chapter 10. Compiled Code

R is a high-level, expressive language. But that expressivity comes at a price: speed. That’s why incorporating a low-level, compiled language like C or C++ can powerfully complement your R code. Although C and C++ often require more lines of code (and more careful thought) to solve the same problem, they can be orders of magnitude faster than R.

Teaching you how to program in C or C++ is beyond the scope of the book. If you’d like to learn, start with C++ and the Rcpp package. Rcpp makes it easy to connect C++ to R. I’d also recommend using RStudio because it has many tools that facilitate the entire process. Start by reading my “High Performance Functions with Rcpp”, a freely available book chapter from Advanced R: it gently introduces the language by translating examples of familiar R code into C++. Next, check out the Rcpp book and the other resources listed in learning more.

C++

To set up your package with Rcpp, run the following:

devtools::use_rcpp()

This will:

• Create an src/ directory to hold your .cpp files.

• Add Rcpp to the LinkingTo and Imports fields in the DESCRIPTION.

• Set up a .gitignore file to make sure you don’t accidentally check in any compiled files (learn more about this in Chapter 13).

• Tell you the two roxygen tags you need to add to your package:

  #' @useDynLib your-package-name
  #' @importFrom Rcpp sourceCpp
  NULL

Workflow

Once you’re set up, the basic workflow should now be familiar:

1. Create a new C++ file, as illustrated ...