Intro, Git, and GitHub

Why we use code and why we should use version control

Author

Matthew DeHaven

Published

January 21, 2026

Welcome to the Course

Welcome to Econ 2020

Applied Economics Analysis

. . .

Instructor

Matthew DeHaven (5th year graduate student)

Myles Ellis (5th year graduate student)

Introductions

What is your name?
Where are from?
What do you think your field in economics will be?
- (purely speculative, not holding you to it!)

A fun one:

What is one of your favorite food spots in Providence?

What is this course?

Course goals
Longer-term assignments
Weekly problem sets
Lecture structure
Class feedback
Class website

Course Goals

Able to replicate published papers in economics
Learn how to program
- Specifically, R and a bit of Python, Julia, HTML
Write clean, documented, reproducible code
Apply software tools and best practices to economic research projects

. . .

Prepare you with practical skills for 2nd year on.

Longer-term assignments

Replication 1

Replicate a published paper in economics

. . .

Final Project and Presentation

Apply what we learn to exploring a research project idea

. . .

Replication 2

Replicate a classmate’s final project

. . .

I will give more information on each of these assignments later.

Weekly Assignments

One “problem set” (really, a coding exercise) due each week.

. . .

These will be due:

start of Monday class time

. . .

The goal is to…

practice the material from lectures
learn some new methods on your own

. . .

The first assignment is due next class.

Lecture Structure

The goal for lectures:

Lecture
In class activity or coding exercise
Lecture
Live coding example

. . .

This will adjust depending on the topic being covered.

. . .

Please bring your computers to class!

Class Feedback

You will fill out a survey at the end of each lecture.

. . .

These will ask some questions about…

material comprehension
teaching feedback (i.e. things I can do better)

. . .

These are not graded, but filling them out counts as your participation grade.

If you miss class, do not fill out the survey.

Course Website

All of the material for this course lives on a course website.

course schedule
lecture slides
assignments
guides

I will be updating the website throughout the course.

Course Website Tour

Link on Canvas and on my website.

Why code?

Why do we program instead of simply open Excel, highlight the right data, hit the “regress” button?

. . .

Many reasons, but a main one…

Programs are reproducible documents of the steps we took and decisions we made.

. . .

Reproducibility is becoming more and more important in economics.

Replicatibility vs Reproducibility

Reproducibility: same data \(\implies\) same results

Computational Reproducibility: same code + same data \(\implies\) same results
Recreate Reproducibility: recreate code + same data \(\implies\) same results

Replicability: new data \(\implies\) same results

. . .

I will be using these terms interchangeably, but we are focused on reproducubility, specifically computational reproducibility.

. . .

More categories and desription in A framework for evaluation reproducibility and replicability in economics (2023), Dreber, Anna, Magnus Johannesson.

Importance of Replication

Writing reproducible code allows

others to trust your results.
you to know what you did six months ago.

Before the Current Version

Code keeps a reproducible state of our current project.

But what about the decisions we made before hand?

What if we decide we preferred the model we ran 6 months ago?

. . .

One solution: make copies of all your files with “_vXX”
Better solution: use version control

Version Control and Git

Version Control

Version control keeps track of files at different states (“commits”),

. . .

by storing the differences between the file in one “commit” and the next.

. . .

This allows us to

see the history of any file
revert to any point in that history

Why do we need version control?

Why do we need version control?

To the right, a hypothetical project directory
It runs some regressions, makes output LaTeX files
Which file creates the second version of the output?
Is the “_CA” or “_MD” files more recent?
Which is the current file to use?

project/
- code/
  - run_regs.R
  - run_regs_v2.R
  - run_regs_v2_MD.R
  - run_regs_v2_CA.R
  - run_regs_20240101.R
- output/
  - reg_results.tex
  - reg_results_v2.tex

What is Git?

An implementation of version control
Very popular among programmers
Operate through command line or choose from many easy to use GUIs
- We will be using VS Code’s built in Git extension
Additional tools (namely, GitHub) for collaborating with others

Git Process

graph LR
    A[Edited<br>Files] -- "git add" --> B(Staged<br>Changes)
    B -- "git commit" --> C[(Local<br>Repository)]

git add: select which edited files to include in the next commit

git commit: save staged changes as a new commit in the repository

always includes a commit message describing the changes

Git Commit Graph

Once you have some commits, you can view the history of your repository.

Git File Revisions

And we can look at the difference between the current version of the file, and any of the saved commits.

. . .

The changes from the “Updated data source” commit:

. . .

GitHub

How is GitHub different from Git?

Git: version control stored on your computer

. . .

GitHub: version control stored online

. . .

backups your project

. . .

allows collaboration with others

. . .

let’s you share your work

GitHub in this course

We will be using GitHub extensively in this course.

. . .

All of your problem sets will be submitted on GitHub.

. . .

Your final project will be a GitHub respository,

. . .

and will be graded in part by its commit history.

. . .

And we will see how GitHub also makes it easy to host websites.

Git and GitHub

From now on, think of Git and GitHub grouped together.

We won’t use one without the other.

Class Activity

Partner with someone near you
Navigate to Grant McDermott’s GitHub page: https://github.com/grantmcdermott
- A principal economist at Amazon, some of this course is based off of a course he taught
Explore a commit history on one of his repositories
- Click on a repository
- Click on “Commits” on a repository page
- Click on a few commits to see the changes made
Be prepared to share with the class one commit
- What did he change in that commit?

Git and GitHub Details

Initializing Git from GitHub
Git Workflow
- Staging
- Commit messages
- Committing
- Pushing to GitHub
Ignoring files

Initializing a GitHub Repository

Create a new repository on GitHub
Copy the repository URL
Clone the repository to your computer
- “clone” means copy the repository from GitHub to your computer

graph LR

  A[(GitHub<br>Repository)] -. "git clone" .-> B[(Local<br>Repository)]

  subgraph Local Computer
  B[(Local<br>Repository)]
  end

. . .

This is the process you will be using for your homework assignments. I will show an example at the end of class.

Committing file changes

Once you edit a file, Git will notice a change.

I edited my previous script “run_regressions.R” and added “new_script.R”.

Staging changes

Once you are at a point to commit, first you stage your changes.

. . .

This allows you to select the changes you wish to commit at this time.

. . .

Commit Messages

You always have to write a message with every commit.

. . .

They also have a character length limit, so they have to be short.

. . .

But try to make them useful!

. . .

Don’t use:

“edits”
“hi”
“acdfasdfadaf”

Do use:

“Reran with data for 2020”
“Robust check for table 1”
“Made reg loop more efficient”

Commit Messages

Here’s one for our example:

Remember, you will be looking back at your Git messages, so try to write something helpful!

Committing

Then you hit “commit”!

And a new commit is added to the history.

Pushing commits

Now that you have a new commit you can push it to GitHub.

You can push after one or multiple local commits.

. . .

graph LR
  subgraph Local Computer
  A[Edited<br>Files] -- "git add" --> B(Staged<br>Changes)
  B -- "git commit" --> C[(Local<br>Repository)]
  C --> A
  end

  C -- "git push" --> D[(GitHub<br>Repository)]

What files should be tracked?

Always track:

code, raw data, documentation (readme files, etc.)

Sometimes track:

intermediate data, output files (tables, figures, etc.)

Never track:

very large files (> 100 MB)
- Can set up Git Large File Storage (LFS) for some large files
private information (API keys, etc.)

How to ignore files with Git

For files you do not want Git to track, use a .gitignore file.

Simply a text file named .gitignore in your project folder.

List the files one by one
List of folders
Use regular expressions for patterns (we’ll cover regex later)

large-output-file.RDS

some-dataset.csv

a-whole-folder/

*.pdf

How Git stores files

When you initialize Git in a folder,

a hidden .git folder is created
a copy of every current file and subfolder is stored

. . .

When you commit changes,

a new copy of every changed file is stored
along with the original file

When Should You Commit?

After completing a logical unit of work
- “Fixed bug in regression loop”
- “Added summary statistics table”
Before trying something experimental
Multiple times per work session
- Not just at the end of the day!

Think: “If I had to explain what I just did to someone, would it be one clear sentence?”

Coding Example

A tour of github.com
Showing the Git workflow
- new repository
- clone to local computer
- edit files
- stage changes
- write message
- commit
- push
Take a look at Assignment 1 together