Violin plot basics

Violin plots are similar to histograms and box plots in that they show an abstract representation of the probability distribution of the sample. Rather than showing counts of data points that fall into bins or order statistics, violin plots use kernel density estimation (KDE) to compute an empirical distribution of the sample. That computation is controlled by several parameters. This example demonstrates how to modify the number of points at which the KDE is evaluated (points) and how to modify the band-width of the KDE (bw_method).

For more information on violin plots and KDE, the scikit-learn docs have a great section: https://scikit-learn.org/stable/modules/density.html

import numpy as np
import matplotlib.pyplot as plt

# Fixing random state for reproducibility
np.random.seed(19680801)


# fake data
fs = 10  # fontsize
pos = [1, 2, 4, 5, 7, 8]
data = [np.random.normal(0, std, size=100) for std in pos]

fig, axs = plt.subplots(nrows=2, ncols=5, figsize=(10, 6))

axs[0, 0].violinplot(data, pos, points=20, widths=0.3,
                     showmeans=True, showextrema=True, showmedians=True)
axs[0, 0].set_title('Custom violinplot 1', fontsize=fs)

axs[0, 1].violinplot(data, pos, points=40, widths=0.5,
                     showmeans=True, showextrema=True, showmedians=True,
                     bw_method='silverman')
axs[0, 1].set_title('Custom violinplot 2', fontsize=fs)

axs[0, 2].violinplot(data, pos, points=60, widths=0.7, showmeans=True,
                     showextrema=True, showmedians=True, bw_method=0.5)
axs[0, 2].set_title('Custom violinplot 3', fontsize=fs)

axs[0, 3].violinplot(data, pos, points=60, widths=0.7, showmeans=True,
                     showextrema=True, showmedians=True, bw_method=0.5,
                     quantiles=[[0.1], [], [], [0.175, 0.954], [0.75], [0.25]])
axs[0, 3].set_title('Custom violinplot 4', fontsize=fs)

axs[0, 4].violinplot(data[-1:], pos[-1:], points=60, widths=0.7,
                     showmeans=True, showextrema=True, showmedians=True,
                     quantiles=[0.05, 0.1, 0.8, 0.9], bw_method=0.5)
axs[0, 4].set_title('Custom violinplot 5', fontsize=fs)

axs[1, 0].violinplot(data, pos, points=80, vert=False, widths=0.7,
                     showmeans=True, showextrema=True, showmedians=True)
axs[1, 0].set_title('Custom violinplot 6', fontsize=fs)

axs[1, 1].violinplot(data, pos, points=100, vert=False, widths=0.9,
                     showmeans=True, showextrema=True, showmedians=True,
                     bw_method='silverman')
axs[1, 1].set_title('Custom violinplot 7', fontsize=fs)

axs[1, 2].violinplot(data, pos, points=200, vert=False, widths=1.1,
                     showmeans=True, showextrema=True, showmedians=True,
                     bw_method=0.5)
axs[1, 2].set_title('Custom violinplot 8', fontsize=fs)

axs[1, 3].violinplot(data, pos, points=200, vert=False, widths=1.1,
                     showmeans=True, showextrema=True, showmedians=True,
                     quantiles=[[0.1], [], [], [0.175, 0.954], [0.75], [0.25]],
                     bw_method=0.5)
axs[1, 3].set_title('Custom violinplot 9', fontsize=fs)

axs[1, 4].violinplot(data[-1:], pos[-1:], points=200, vert=False, widths=1.1,
                     showmeans=True, showextrema=True, showmedians=True,
                     quantiles=[0.05, 0.1, 0.8, 0.9], bw_method=0.5)
axs[1, 4].set_title('Custom violinplot 10', fontsize=fs)


for ax in axs.flat:
    ax.set_yticklabels([])

fig.suptitle("Violin Plotting Examples")
fig.subplots_adjust(hspace=0.4)
plt.show()

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References

The use of the following functions and methods is shown in this example:

import matplotlib
matplotlib.axes.Axes.violinplot
matplotlib.pyplot.violinplot

Out:

<function violinplot at 0x7f5f32b88ca0>