A meaningful file structure for R projects

Have you ever tried to find your way around in the file structure of an already existing project? To separate relevant from obsolete files in a historically grown directory? To find out in which order existing scripts should be executed?

To make all this easier, it helps to have a consistent file and folder structure across your projects. You should have some experience with R, RStudio and maybe package development to find this useful. We also believe our structure is of special interest for those who work with R in a team.

Similar to coding style guidelines, it is more important that you can agree on one than picking the best one.

A useful file structure

There is of course not the one and only best file structure. The following figure shows our solution for a project’s file structure:

Fig. 1 – A useful file structure

When you are working with RStudio, you will recognize the .Rproj file. This file determines the project root and also the working directory for R sessions. This has the advantage that all file paths can be set relative to the project’s root directory. You can move the whole project folder and all paths in your code will still be working!

The first folder is called RScripts. It contains all scripts written in R. Typical examples are scripts for data preparation and data analysis. We recommend to number the scripts in the order they need to be executed. See also our other article "INWT's guidelines for R code" for guidelines for script files.

Scripts may produce outputs. Outputs can be data, as in spreadsheet-like tabular form, or any other form like graphics, tables as .tex files, etc. These outputs are then stored either in a data or a results folders. The distinction between the two folders is sometimes fuzzy, but in general the data folder stores everything the data analysis is based on. The results folder is used to store the final outputs of an analysis and not some intermediate steps. This folder may live inside the data folder or also in the root.

Files in this folder are often used to cache results which are later needed in an R Markdown report. Although knitr provides its own caching mechanism, in many projects it is better to decouple single computations so editing of reports is simpler.

All data (raw and processed) live in the folder data. This includes different file formats such as .Rdata, .xlsx or .csv. These data are kept separate from any R package to enable fast deployment cycles; e.g., when they are large, this can be an issue. Also they are not checked in into version control. In most scenarios these data files are the output of some R script doing time-consuming data transformations or extracting data from external resources (think of databases or crawlers). Hence these files can always be reconstructed; this folder is never used as a persistent file storage.

The reports folder contains the reports we create with R Markdown. For these reports we have our own R Markdown templates and ggplot2 theme. Complying to corporate design guidelines has never been easier.

Where does the package live?

Virtually all of our projects include an R package. R packages have their own specific file and folder structure, but where should these files be located? There are two options: Either all package files are stored in an own folder (called for example package as in fig. 1), or they are stored in the project’s root directory (as in fig. 2).

Which way should be preferred depends on the nature of the project. A data analysis is always backed up by a package. Even if the functions are never used in any other project, we still need documentation and unit tests for R code. Furthermore dependencies need to be installed and maintained across the team and machines. So in an analysis, e.g., forecasting sales or computing a customer lifetime value, the package lives in its own folder. This also avoids a conflict: In general, you will have a data folder in an analysis project. Packages also include a folder named data, so R would try to include your data folder when building the package. This may not be what you want.

In projects where package development is the main task, the package lives in the project root. This is the case for our INWTUtils package or in general when packages are used to provide tools used across projects.

Fig. 2 – A file structure including a package

Work in a sandbox

We install all R packages – our own packages and those from CRAN – on a network drive. Thus, everyone in the team has access to the same package versions. But if someone is working on one of our packages, it is not desirable that every little change appears immediately on the network drive: It could contain bugs and disrupt the colleagues’ work.

To solve this problem, we always work in a sandbox when making changes to a package. More precisely, every time we build a new version of the package, it is not deployed to the network drive, but into a particular folder you can see in figure 1: libLinux and libWin (depending on the operating system). This means that everything we try out remains in a self-contained environment without causing any change outside. We need the distinction for OSs because users may work on user-specific network drives but from different machines (8 threads and 16 GB RAM on Windows is not enough? How does 32 threads and 250 GB RAM sound?). This is however just a small boost for developer productivity.

How does RStudio know where to install the package when we build it? The .Rprofile file is responsible for this task. It is always sourced when you open R. Our .Rprofile changes the default installation directory in your R project to libLinux resp. libWin. An example file can be seen here. In addition, the folders libLinux and libWin are a good place to install packages you just want to try out without affecting the network drive.

Even if you don’t share a package directory on a network drive with your colleagues, working in a sandbox can have advantages. You can for example work on your own package without affecting the stable version in your user library.

Just get started!

It’s still hard enough to orient yourself in a project where many people left their mark on. But it becomes easier if the file structure is consistent and well thought through. And this also forces you to work in such a way that your colleagues don’t get lost in your files and folders.

To get started, we use the INWTUtils package which can instantiate folders and package structures complying to these standards. This is a good way to get everyone on the team into using it.

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