Violin plots in Matplotlib


Martin McBride, 2022-06-24
Tags matplotlib violin plot
Categories matplotlib

A violin pot is similar to a box plot. The difference is that, for each data point, it displays a small histogram to show the data variance. This gives a bit more detail than a box plot, which only shows teh quartiles.

That doesn't automatically make violin pots better than box plots, because sometimes a box plot can be clearer and easier to read.

Example violin plot

Here is an example:

For a violin plot, the main line of each figure goes from the minimum value to the maximum value, including any outliers. The shaded area indicates the distribution of values within that range.

Here is the code:

import matplotlib.pyplot as plt
import csv

with open("2009-temp-monthly-list.csv") as csv_file:
    csv_reader = csv.reader(csv_file, quoting=csv.QUOTE_NONNUMERIC)
    temperature = list(csv_reader)

month_names = ["J", "F", "M", "A", "M", "J",
               "J", "A", "S", "O", "N", "D"]

months = range(12)

plt.title("Temperature violin plot 2009")
plt.xlabel("Month")
plt.ylabel("Temperature")
plt.violinplot(temperature, positions=months)
plt.xticks(months, month_names)
plt.show()

The code is here on github, in the file violinplot_temperatures.py.

The only change compared to the box plot code is the call to violinplot rather than boxplot.

If you found this article useful, you might be interested in the course Introduction to Matplotlib by the same author.

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