The File Ecosystem

There are a core set of files that R uses that you’ll likely run into and want to know the meaning of.

.R

The base of the programming language, the .R file is the simplest and most commonly used file for writing a program in R. A set of commands in the file, executed in order by the computer, provides the user with a reproducible way of repeating an analysis.

In .R files, all written text is assumed to be written in the syntax and language of R, such as this:

    x <- 2 + 2
    print("x is ", x)

## [1] "x is "

To write comments or notes to yourself or other future users of the file, use the pound symbol or “hashtag” (#) to tell R to ignore that part of the text.

Example: If we wanted to leave ourselves a comment telling us what our code will do we could write

    x <- 2 + 2
    # print the value of x to the console
    print(x)

## [1] 4

.Rmd

The .rmd file is a special hybrid between an R file .R and a markdown file .md. This file type gives us flexibility to use both R programming, and write in a normal text editor document like a Microsoft Word doc. Markdown is a lightweight markup language used for creating formatted text.

In short, we can write both normal text (such as methods or results), *and* include chunks of code in the same file. This is very handy for writing reports and assignments.

.Rproj

The last important file you’ll use once you’re more familiar with R is the .rproj file. This file formats an R Project, which is a component of ensuring a reproducible analysis. This file acts to store information about your R Project, as well as point to the directory you have stored your analysis in. This file can also be used as a shortcut for opening the project directly from the filesystem. More about this file type can be found in R Projects.