Using R for Introductory Statistics : John Verzani

Appendix E 378}while(x > 0) {ret = ret*xx = x−1}return(ret)There is no real savings here. In fact, neither function is a very good way to perform thistask.E.3 Using files and a better editorIf you plan on doing any significant programming in R, then it is worthwhile tofamiliarize yourself with using external files to store your work (rather than the defaultworkspace) and using a different editor to facilitate interaction between the external filesand an R process.E.3.1 Using an external editorThe edit () function makes small changes easy, but the changes are not saved in aconvenient way for future reference. They can be saved in the workspace, but this canbecome quite cumbersome. It is often better to keep functions in files in the workingdirectory. Many functions can be kept in a single file, or each one in its own file.Commands can also be stored in a file for subsequent editing.The basic idea is to edit the file and then have its contents parsed and evaluated in Rline by line. This last step is done with the function source (). This process is repeateduntil you are satisfied.For example, you can save the hello function in a file called “hello.R" using a texteditor of your choice (e.g., Notepad) and then read the contents in using the source()function, as in> source("hello.R")Specifying the file name can be done conveniently with the file. choose () function. Moredetails on specifying a file are given in Chapter 1.Better text editorsIf you are going to be programming a lot in R, it makes sense to use an editor well suitedto the job. The default editor in Windows, Notepad, is quite primitive; the default editor(often vi) in UNIX may be too cryptic. The editor can be changed using options (), but towhich one? Good editors should do some work for you. For writing programs in R whatis desired are features such as on-the-fly code formatting, syntax highlighting, integrationwith an R process, and debugging help.There are several choices. The most advanced and powerful is a combination ofEmacs (either XEmacs, http://www.xemacs.org/, or GNU Emacs, http://www.gnu.org/);and ESS, (http://www.analytics.Washington.edu/statcomp/projects/ess/). Emacs is a text