We created a usable package by just

  • Creating a directory with a subdirectory R
  • Putting some .R files in the R subdirectory
  • Creating a DESCRIPTION file with the package name and a version number.

We can build the .tar.gz package file and give it to friends to install, but it’s still not a proper R package. We need to do a few more things.

  • Fill out the DESCRIPTION file.
  • Create a NAMESPACE file.
  • Add some documentation.

Filling out the DESCRIPTION file

Our DESCRIPTION file had just two lines. We need to add a few more: a title, a description, an author, and a maintainer (usually one of the authors). It’s also a good idea to include the date. It should look something like this:

Package: brocolors
Version: 0.1
Date: 2014-08-27
Title: Karl Broman Colors
Description: Colors that Karl Broman uses in figures.
Author: Karl W Broman <kbroman@biostat.wisc.edu>
Maintainer: Karl W Broman <kbroman@biostat.wisc.edu>

The title should be short. The description should be a sentence or two; it can span multiple lines. The Maintainer field should include an email address, surrounded by < >. The author field doesn’t need email addresses.

A bunch more things can be put in the DESCRIPTION file, but this is sufficient for now.

Creating a NAMESPACE file

Creating a package NAMESPACE file has long been one of the more painful aspects of building an R package. I dragged my feet on these NAMESPACE files for years. (It’s no longer so painful, as we’ll see shortly.)

With the huge growth in the number of R packages, it became important to avoid naming conflicts among packages: two packages might have the same name for totally different functions, particularly with little helper functions. With a NAMESPACE file, you indicate which functions are to be available to users and which are to be strictly internal. By hiding the little helper functions, there’s less chance of naming conflicts.

A minimal NAMESPACE file is pretty easy, though. You just need one line.

# Export all names
exportPattern(".")

Okay, that’s two lines. But the first line is just a comment.

So the simplest step towards making your R package a proper package is to create a plain text file called NAMESPACE containing these lines and put it in your package directory.

Your package will then look like this.

It’s still not a proper package (in that we still need to write some documentation), but you can now build and install it with devtools.

Documentation

It’s not a proper package until you’ve added documentation. The documentation will sit in a man subdirectory (man for “manual”), and has to be in a special .Rd (Rd for “R documentation”) format, with .Rd file for each function in the package. The .Rd format is rather LaTeX-like and so ugly to prepare and maintain.

But, you don’t have to create those .Rd files yourself. Roxygen2 is an R package that makes it much easier to create R documentation for your R package. You write comments within your .R files, in a specially structured way, describing the inputs and outputs and so forth for each function, and then Roxygen2 will create the .Rd files for you. Roxygen2 will also create the NAMESPACE file for you.

I’ll explain the use of Roxygen2 next.

Software license

And actually, there’s one more thing (after the documentation) that you need to do before your package is proper. You need to pick a license for the software and specify the license in the DESCRIPTION file. This is, perhaps, an even more ugly topic than NAMESPACE files. I’ll explain it a bit later.


Homework

Fill out the DESCRIPTION file for your package and add a minimal NAMESPACE file. Try building and installing it with devtools.

Then go to the page about writing documentation with Roxygen2.