Chord diagram with Python and the chord library

A chord diagram is a chart type allowing to visualise flows between entities. The chord library is probably the best way to build a chord diagram with Python. This blogpost will guide you through its usage.

Input dataset

The dataset considered in this page provides the number of people migrating from one country to another. Data used comes from this scientific publication already discussed on data-to-viz.com.

The data is stored online here. Let's load it into Python as follow:

# Pandas is gonna be used to read the csv file stored on the web:
import pandas as pd

# Load dataset from github
data = pd.read_csv("https://raw.githubusercontent.com/holtzy/data_to_viz/master/Example_dataset/13_AdjacencyDirectedWeighted.csv", sep=" ")
data

# Create a list of all the items in the diagram
names = data.columns.values

data = data.values.tolist()
data

[[3.142471,
  0.0,
  2.107883,
  0.0,
  0.540887,
  0.15598800000000002,
  0.0,
  0.0,
  0.0,
  0.673004],
 [0.0,
  1.630997,
  0.6012649999999999,
  0.0,
  0.97306,
  0.333608,
  0.0,
  0.380388,
  0.0,
  0.8693110000000001],
 [0.0, 0.0, 2.4014759999999997, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0],
 [0.0, 0.0, 1.762587, 0.8791979999999999, 3.627847, 0.0, 0.0, 0.0, 0.0, 0.0],
 [0.0, 0.0, 1.215929, 0.276908, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0],
 [0.0, 0.0, 0.17037, 0.0, 0.0, 0.190706, 0.0, 0.0, 0.0, 0.0],
 [0.0,
  0.525881,
  1.390272,
  0.0,
  1.508008,
  0.34742,
  1.307907,
  0.0,
  0.0,
  4.902081],
 [0.0,
  0.145264,
  0.468762,
  0.0,
  1.0579040000000002,
  0.278746,
  0.0,
  0.781316,
  0.0,
  0.0],
 [0.0, 0.0, 0.60923, 0.0, 0.0, 0.0, 0.0, 0.0, 1.8705009999999997, 0.0],
 [0.0, 0.0, 0.44962299999999994, 0.0, 0.169274, 0.0, 0.0, 0.0, 0.0, 0.927243]]

What's important to understand here is that the chord library used later needs a matrix as input.

Installing the `chord` library

All the hard work is gonna be tackled by the chord library. This library basically wraps some javascript functions available in a really powerful library called d3.js. But you do not really need to take care about this 🎉

In order to take advantage of this library, we need to use it:

pip install chord

Requirement already satisfied: chord in /opt/anaconda3/lib/python3.8/site-packages (0.10.0)
Note: you may need to restart the kernel to use updated packages.

Most basic chord diagram

Let's start with the most simple chord diagram that can be built with this library

# Import the library
from chord import Chord


# Basic cord diagram
# TODO THIS WON'T WORK BECAUSE INPUT TYPE ISNT RECOGNIZE
# Chord(data, names).to_html("../../static/interactiveCharts/chord-diagram-chord-library.html")

matrix = [
    [0, 5, 6, 4, 7, 4],
    [5, 0, 5, 4, 6, 5],
    [6, 5, 0, 4, 5, 5],
    [4, 4, 4, 0, 5, 5],
    [7, 6, 5, 5, 0, 4],
    [4, 5, 5, 5, 4, 0],
]


names = ["Action", "Adventure", "Comedy", "Drama", "Fantasy", "Thriller"]

matrix

[[0, 5, 6, 4, 7, 4],
 [5, 0, 5, 4, 6, 5],
 [6, 5, 0, 4, 5, 5],
 [4, 4, 4, 0, 5, 5],
 [7, 6, 5, 5, 0, 4],
 [4, 5, 5, 5, 4, 0]]

Chord(matrix, names).to_html("../../static/interactiveCharts/chord-diagram-chord-library.html")

%%html
<iframe src="../../interactiveCharts/chord-diagram-chord-library.html" width="800" height="600" title="Chord diagram with the chord library" style="border:none"></iframe>

Chord Diagram

Network

Sankey

Arc Diagram

Edge Bundling

🚨 Grab the Data To Viz poster!

Do you know all the chart types? Do you know which one you should pick? I made a decision tree that answers those questions. You can download it for free!

Chord diagram with Python and the chord library

Input dataset

Installing the chord library

Most basic chord diagram

Flow

🚨 Grab the Data To Viz poster!

Installing the `chord` library