Loading Packages

By default, not all packages are loaded into R. If you try to use a function from a package that hasn’t been loaded, you’ll get an error:

> # try to use rpart before loading it
> fit <- rpart(Kyphosis ~ Age + Number + Start, data=kyphosis)
Error: could not find function "rpart"

To load a package in R, you can use the library() command. For example, to load the package rpart (which contains functions for building recursive partition trees), you would use the following command:

> library(rpart)

(There is a similar command, require(), that takes slightly different arguments. For more about require, see the R help files.)

If you’re more comfortable using a GUI, you can browse for packages and load them using the GUI. If you choose to use this interface to find packages, make sure that you include the appropriate library command with your scripts to prevent errors later.

Loading Packages on Windows and Linux

On Microsoft Windows, you can use the library function to load packages. Alternatively, you can select “Load package” from the Packages menu in the GUI. This will bring up a window showing a list of packages that you can choose to load.

Loading Packages on Mac OS X

The Mac OS X R environment is a little fancier than the other versions. Like the other versions, you can use the library() function. Otherwise, you can select Package Manager from the “Packages & Data” menu. The Package Manager UI, as shown in Figure 4-1, lets you see which packages are loaded, load packages, and even browse the help file for a package.

Mac OS X Package Manager

Figure 4-1. Mac OS X Package Manager

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