The Art of R Programming

Let’s try it out:

> joe

Joe has a salary of 55000 and is in the union

9.3 S3 Versus S4...............................................................

The type of class to use is the subject of some controversy among R program-

mers. In essence, your view here will likely depend on your personal choice

of which you value more—the convenience of S3 or the safety of S4.

John Chambers, the creator of the S language and one of the central

developers of R, recommends S4 over S3 in his bookSoftware for Data Anal-

ysis(Springer, 2008). He argues that S4 is needed in order to write “clear

and reliable software.” On the other hand, he notes that S3 remains quite

popular.

Google’s R Style Guide, which you can find athttp://google-styleguide

.googlecode.com/svn/trunk/google-r-style.html, is interesting in this regard. Google

comes down squarely on the S3 side, stating “avoid S4 objects and methods

when possible.” (Of course, it’s also interesting that Google even has an R

style guide in the first place!)

NOTE A nice, concrete comparison of the two methods is given in Thomas Lumley’s

“Programmer’s Niche: A Simple Class, in S3 and S4,”R News, April 1, 2004,

pp. 33–36.

9.4 Managing Your Objects.....................................................

As a typical R session progresses, you tend to accumulate a large number of

objects. Various tools are available to manage them. Here, we’ll look at the

following:

• Thels()function


• Therm()function


• Thesave()function


• Several functions that tell you more about the structure of an object,
  such asclass()andmode()


• Theexists()function

9.4.1 Listing Your Objects with the ls() Function..........................

Thels()command will list all of your current objects. A useful named argu-

ment for this function ispattern, which enableswildcards. Here, you tellls()

to list only the objects whose names include a specified pattern. The follow-

ing is an example.

226 Chapter 9