1.1 What is R?

First, R is a programming language. If you write code in R and save it, it will remain useful and repeatable for as long as you have a program that can run your code, which brings us to the second layer. R is a code interpreter. You can run R at the command line and either enter code directly, or tell it to run code files, or scripts, that you saved earlier in order to analyze data, run simulations, or anything else you can think of. You can download R the code interpreter from www.r-project.org. Finally, RStudio is an excellent (and constantly improving) development interface for R, providing easy access to script files, help and documentation, plotting and figures, code autocomplete and syntax help, among many other useful features. You can download RStudio from www.rstudio.com.

It is important to also note that R is free and open source. This means that you can learn and use a fully featured statistical computing framework and continue to use it for free after you finish this class and even school as a whole. Additionally, R is incredibly extensible. Part of why R is so widely used is because of its extensive library of functions. When someone comes up with a new method, they (or someone who wants to use it in R) will often implement the method as a collection of functions in R called a package. R has a central repository of packages called the Comprehensive R Archive Network or CRAN for short.