R packages

Learn how to add functionality to R with packages
Author

Stefano Coretta

Published

June 27, 2024

Pre-requisites

1 R packages

Important

When working through the Notebook entries, always make sure you are in the course Quarto Project you created earlier.

You know you are in a Quarto Project because you can see the name of the Project in the top-right corner of RStudio, next to the light-blue cube icon.

If you see Project (none) in the top-right corner, that means you are not in a Quarto Project.

To make sure you are in the right Quarto project, you can open the project by going to the project folder in File Explorer (Win) or Finder (macOS) and double click on the .Rproj file.

When you install R, a library of packages is also installed. Packages provide R with extra functionalities, usually by making extra functions available for use. You can think of packages as “plug-ins” that you install once and then you can “activate” them when you need them. The library installed with R contains a set of packages that are collectively known as the base R packages, but you can install more any time!

Note that the R library is a folder on your computer. Packages are not installed inside RStudio. Remember that RStudio is just an interface.

You can check all of the currently installed packages in the bottom-right panel of RStudio, in the Packages tab. There you can also install new packages.

R library and packages

  • The R library contains the base R packages and all the user-installed packages.

  • R packages provide R with extra functionalities and are installed into the R library.

Extra: Where is my R library?

If you want to find the path of the R library on your computer, type .libPaths() in the Console. The function returns (i.e. outputs) the path or paths where your R library is.

1.0.1 Install packages

You can install extra packages in the R library in two ways:

  1. You can use the install.packages() function. This function takes the name of the package you want to install as a string, for example install.packages("cowsay").
Warning

If you install a package with the function install.packages(), do so in the Console! Do not include this function in your scripts (this is because you install packages only once, see below).

  1. Or you can go the Packages tab in the bottom-right panel of RStudio and click on Install. A small window will pop up. See the screenshot below.

Go ahead and try to install a package using the second method. Install the cowsay and the fortunes packages (see picture above for how to write the packages). After installing you will see that the package fortunes is listed in the Packages tab.

Install packages

To install packages, go to the Packages tab of the bottom-right panel of RStudio and click on Install.

In the “Install packages” window, list the package names and then click Install.

Warning

You need to install a package ONLY ONCE! Once installed, it’s there for ever, saved in the R library. You will be able to use all of your installed packages in any RStudio/Quarto project you create.

1.0.2 Attach packages

Now, to use a package you need to attach the package to the current R session with the library() function. Attaching a package makes the functions that come with the package available to us.

Warning

You need to attach the packages you want to use once per R session.

Note that every time you open RStudio, a new R session is started.

Let’s attach the cowsay and fortunes packages. Write the following code at the top of your R script, before all the other code you wrote.

library(cowsay)
library(fortunes)

Note that library(cowsay) takes the name of the package without quotes, although if you put the name in quotes it also works. You need one library() function per package (there are other ways, but we will stick with this one).

Attaching packages

Packages are attached with the library(pkg.name) function, where pkg.name is the name of the package.

It is customary to put all the packages used in the script at the top of the script.

Now you can use the functions provided by the attached packages. Try out the say() function from the cowsay package.

Write the following in your R script and run it!

say("hot diggity", "frog")

(I know, the usefulness of the package might be questionable, but it is fun!)

Warning

Remember, you need to install a package only once but you need to attach it with library() every time you start R.

Think of install.packages() as mounting a light bulb (installing the package) and library() as the light switch (attaching the package).

1.1 Package documentation

To learn what a function does, you can check its documentation by typing in the Console the function name preceded by a ? question mark. Type ?say in the Console and hit ENTER to see the function documentation. You should see something like this:

The Description section is usually a brief explanation of what the function does.

In the Usage section, the usage of the function is shown by showing which arguments the function has and which default values (if any) each argument has. When the argument does not have a default value, NULL is listed as the value.

The Arguments section gives a thorough explanation of each function argument. (Ignore … for now).

How many arguments does say() have? How many arguments have a default value?

Default argument values allow you to use the function without specifying those arguments. Just write say() in your script on a new line and run it. Does the output make sense based on the Usage section of the documentation?

The rest of the function documentation usually has further details, which are followed by Examples. It is always a good idea to look at the example and test them in the Console when learning new functions.

Quiz 1
Which of the following statements is wrong?

This was a question about terminology. In R, you attach packages from the library using (confusingly) the library() function.

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