10 Collaborating using Git

10.1 Learning Objectives

In this lesson, you will learn:

• New mechanisms to collaborate using git
• What is a Pull Request in Github
• How top contribute code to colleague’s repository using Pull Requests
• What is a branch in git
• How to use a branch to organize code
• What is a tag in git and how is it useful for collaboration

10.2 Pull requests

We’ve shown in other chapters how to directly collaborate on a repository with colleagues by granting them write privileges as a collaborator to your repository. This is useful with close collaborators, but also grants them tremendous latitude to change files and analyses, to remove files from the working copy, and to modify all files in the repository.

Pull requests represent a mechanism to more judiciously collaborate, one in which a collaborator can suggest changes to a repository, the owner and collaborator can discuss those changes in a structured way, and the owner can then review and accept all or only some of those changes to the repository. This is useful with open source code where a community is contributing to shared analytical software, to students in a lab working on related but not identical projects, and to others who want the capability to review changes as they are submitted.

To use pull requests, the general procedure is as follows. The collaborator first creates a fork of the owner’s repository, which is a cloned copy of the original that is linked to the original. This cloned copy is in the collaborator’s GitHub account, which means they ave the ability to make changes to it. But they don’t have the right to change the original owner’s copy. Pull requests are a mechanism for someone that has a forked copy of a repository to request that the original owner review and pull in their changes. This allows them to collaborate, but keeps the owner in control of exactly what changed.

10.2.1 Exercise: Create and merge pull requests

In this exercise, work in pairs. Each pair should create a fork of their partner’s training repository, and then clone that onto their local machine. Then they can make changes that forked repository, and, from the GitHub interface, create a pull request that the owner can incorporate.

10.3 Branches and tags

Branches are a mechanism to isolate a set of changes in their own thread, allowing multiple types of work to happen in parallel on a repository at the same time. These are most often used for trying out experimental work, or for managing bug fixes for historical releases of software. Here’s an example graph showing a branch2.1 that has changes in parallel to the main branch of development:

The default branch in almost all repositories is called master, and it is the branch that is typically shown in the GitHub interface and elsewhere. There are many mechanisms to create branches. The one we will try is through RStudio, in which we use the branch dialog to create and switch between branches.

10.3.1 Exercise:

Create a new branch in your training repository called exp-1, and then make changes to the RMarkdown files in the directory. Commit and push those changes to the branch. Now you can switch between branches using the github interface.