Conan Mercer Applied Scientist

Graphing in Python, The Pie Chart

11 Jul 2020 - Conan Mercer

The Basics

Creating informative plots that look appealing is a very useful skill in any STEM related field of work or study. Like most I used Excel for many years, but it was in post graduate school that I looked into using more sophisticated plotting methods to more accurately display the information I was generating.
A quick bit of research lead me to Python, and an associated library called MatPlotLib. Here are some examples of how to plot using Python. For a guide on how to install and setup the correct environment to begin using MatPlotLib, look here.

Code for the most basic Pie Chart

Figure 1 - Basic pie chart

Aesthetics

The previous pie chart did little in the way of effort towards presentation. MatPlotLib is a very powerful library that can be manipulated and customized to a large degree. Below in Figure 2 we use the same data as in Figure 1, however this time we punch a hole in the middle to give resemblance to a donut, we also add a title and change the colour scheme. Also present in the code is a method to output the pie chart, with two options, the file path and also the desired resolution in dots per inch (dpi).

Code for an aesthetic Colour Pie Chart

Figure 2 - Colour pie chart

Sometimes it might not be appropriate to use colour. An obvious example is that people with colour blindness may have difficulty differentiating between parts of a plot. Another is that colour is a subjective entity, some may like the colours you choose, others may not. To rule these problems out I often use a gray scale to show differences between data sets, see Figure 3.

Code for an aesthetic Grey Scale Pie Chart

Figure 3 - Grey Scale pie chart