Social Network Analysis for Computer Scientists

The main goal of this lab session is to become familiar with NetworkX (a Python package to analyze networks for research purposes).
All relevant information on NetworkX can be found in the NetworkX online documentation.

Your Python environment

For this lab session, you need a working Python environment. For this, there are two options:

1. Use your own self-installed Python environment, and choose your own editor and way of running code (via the command line, an IDE or an interactive notebook). Proceed to Instructions for today
2. Alternatively, you can use the desktop machines in the student computer rooms.
   One easy way to create a Python environment on the university computers, is to use conda. As of 2024, conda appears to be installed already. Therefore, you can likely skip step 1--3 below, and start at step 4.
   1. Download Miniconda by running the following command in your terminal:
      wget https://repo.anaconda.com/miniconda/Miniconda3-latest-Linux-x86_64.sh
   2. Install Miniconda:
      bash Miniconda3-latest-Linux-x86_64.sh
      The installer will ask you some questions. Normally, the standard location suffices and you do not have to add conda to PATH.
   3. After installation finishes, close your terminal so that the changes take effect. Upon opening a new terminal, activate the conda virtual environment with:
      source miniconda3/bin/activate
      If all goes well, you will see that (base) appears in front of your shell prompt. This means that conda's base environment is active.
   4. Create a new conda environment:
      conda create --name snacs
      And activate it with:
      conda activate snacs
      You might use conda for other courses as well, and version conflicts can arise when you install many packages. Using separate environments prevents this.
      NOTE: some packages can make your conda environment take up a lot of space. So try not to use an unnecessary number of environments with duplicate packages. You can also remove an environment that you don't need anymore, see the conda cheatsheet.
   5. Packages can easily be installed with conda. To install NetworkX, run:
      conda install networkx
   6. Getting started
      • Running code from the command line. Now you should be able to run your code from the command line by typing
        python3 scriptname.py
      • Running code in interactive Jupyter notebook from the university environment:
        conda install -c conda-forge jupyterlab
        After installing that once, the notebook/lab can be started using:
        jupyter lab
(When using Jupyter through SSH, so when it is not running on the machine that you are currently working on, make sure to use port forwarding whilst SSH-ing, using options -g -L 8888:127.0.0.1:8888. Also add options --no-browser and --port=8888 when starting up Jupyter.)

Instructions for today: Lab session on NetworkX

1. Take some time to do the NetworkX tutorial.
2. Have a look at functionality to read and write graphs from/to disk, and in particular learn how to import an edge list. Understand the input format and ways of including things like Weight and other attributes of edges.
3. A lot of the common network metrics you may want to compute are implemented as NetworkX function or NetworkX algorithm. Become familiar with these, for example by computing measures such as degree assortativity, clustering, density, diameter and average distance.
4. While at it, why not take a look at how NetworkX relates to other data formats?
5. Try to load the network from the first lab session (small-gephiready.tsv) into NetworkX, and investigate some characteristic properties of the network, such as the degree distribution and distance distribution. Use theread_edgelist function and remember to select the correct separator (tab), and pay attention to the header of the file.
6. Get the Epinions network from the SNAP repository. You may need to fiddle with the precise header, but it is already in edge list format. Compute some common characteristics such as the degree distribution, and visualize them using appropriate figures or distributions, for example using pyplot/Matplotlib.
7. What are the differences between NetworkX and Gephi in terms of visualization and analysis capabilities?

Done? Proceed with Exercise 2 of Assignment 1.

Looking for a challenge? Check out these three alternatives (that you can also use instead of NetworkX throughout the course, if you prefer (but for which there is less help available)):

• Python igraph, a Python version of the R igraph package.
• Graph-Tool, a python graph analysis toolkit that leaves the hard computation to parallel (OpenMP) C++ code.
• SNAP, which is entirely written in C++ and has many interesting features. Nowadays, there is also a Python version.

Running intro problems regarding prior knowledge on python programming? See the reading material at the bottom of this course website.