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.
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.
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 and 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.
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