Agile R: the packaging system

R's packaging system is the key to staying sane while writing your own R code. R follows agile software development practices such as keeping documentation and code together, and even using documentation as a potential source of executable unit tests. The packaging system provides gentle support to guide you towards those best practices.

Working with R packages (practice)

• Peter Rossi has wonderful resources to bootstrap software engineers into the R packaging system:
  • Start with: Some Useful R Pointers
  • Whether on windowz or not, Making R Packages Under Windows is a wonderfully detailed walk through of the package development tools. You'll also want the test package archive
• Another reason to use packages, is that you can then use R-Forge, R's answer to the Google code project. Collaborative Software Development Using R-Forge, Stefan Theußl and Achim Zeileis, R Journal, 1(1), 2009 explains how to use R-Forge, step by step.
• Creating R Packages, Using CRAN, R-Forge, and local R Archive Networks and Subversion (SVN) Repositories covers packaging from the perspective of collaborative development, discussing how the packaging system relates to CRAN, etc.

Why R's packaging systems works the way it does (theory)

• While not specific to the packaging system, John Chambers Facets of R tells the story of how R evolved the way it did, and therefore why the packaging system is the way it is. The comparison to Java and C++ is very valuable. Note that perl's objects are also functional, although perl is not exclusively object-oriented, unlike R. Btw, that difference is a strength, not a weakness, of both languages. We need different languages for different tasks and different communities.
• Richard Stallman explains that the 'free' in free software should be interpreted as the free in free speech, not free beer. That sort of freedom takes infrastructure. Collaborative Software Development Using R-Forge, Stefan Theußl and Achim Zeileis, R Journal, 1(1), 2009 (mentioned above) does a nice job explaining the role resources like R-Forge play in the lives of collaborative software communities.
• Literate programming refers to the practice of not just keeping documentation and code together, but exploiting that fact in various ways. R's packaging system does so to ensure, for example, that documentation is complete and is consistent with the corresponding code. Python and Perl offer modules (nose and Test::Inline, respectively, that take the process a step further and create tests from code samples in documentation.) See Literate programming for creating and maintaining packages, by Jonathan Rougier, R News, 5(1):35-39, May 2005 for the origins of literate programming in R. The current R CMD check offers much richer literate programming, as discussed in the materials in the previous section.