Boxplot Demo

Example boxplot code

import numpy as np
import matplotlib.pyplot as plt

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

# fake up some data
spread = np.random.rand(50) * 100
center = np.ones(25) * 50
flier_high = np.random.rand(10) * 100 + 100
flier_low = np.random.rand(10) * -100
data = np.concatenate((spread, center, flier_high, flier_low))

fig1, ax1 = plt.subplots()
ax1.set_title('Basic Plot')
ax1.boxplot(data)

Out:

{'whiskers': [<matplotlib.lines.Line2D object at 0x7f08b789f3d0>, <matplotlib.lines.Line2D object at 0x7f08b789f790>], 'caps': [<matplotlib.lines.Line2D object at 0x7f08b789ff70>, <matplotlib.lines.Line2D object at 0x7f08b7b3c460>], 'boxes': [<matplotlib.lines.Line2D object at 0x7f08b7467af0>], 'medians': [<matplotlib.lines.Line2D object at 0x7f08b7b3cd00>], 'fliers': [<matplotlib.lines.Line2D object at 0x7f08b7b3c1f0>], 'means': []}

fig2, ax2 = plt.subplots()
ax2.set_title('Notched boxes')
ax2.boxplot(data, notch=True)

Out:

{'whiskers': [<matplotlib.lines.Line2D object at 0x7f08b76d9130>, <matplotlib.lines.Line2D object at 0x7f08b76d94c0>], 'caps': [<matplotlib.lines.Line2D object at 0x7f08b9146be0>, <matplotlib.lines.Line2D object at 0x7f08b6d855e0>], 'boxes': [<matplotlib.lines.Line2D object at 0x7f08b76d9d90>], 'medians': [<matplotlib.lines.Line2D object at 0x7f08b6d85fa0>], 'fliers': [<matplotlib.lines.Line2D object at 0x7f08b6d85070>], 'means': []}

green_diamond = dict(markerfacecolor='g', marker='D')
fig3, ax3 = plt.subplots()
ax3.set_title('Changed Outlier Symbols')
ax3.boxplot(data, flierprops=green_diamond)

Out:

{'whiskers': [<matplotlib.lines.Line2D object at 0x7f08b7733820>, <matplotlib.lines.Line2D object at 0x7f08b7733dc0>], 'caps': [<matplotlib.lines.Line2D object at 0x7f08b74b3880>, <matplotlib.lines.Line2D object at 0x7f08b74b3640>], 'boxes': [<matplotlib.lines.Line2D object at 0x7f08b7733790>], 'medians': [<matplotlib.lines.Line2D object at 0x7f08b74b3850>], 'fliers': [<matplotlib.lines.Line2D object at 0x7f08b74b3a90>], 'means': []}

fig4, ax4 = plt.subplots()
ax4.set_title('Hide Outlier Points')
ax4.boxplot(data, showfliers=False)

Out:

{'whiskers': [<matplotlib.lines.Line2D object at 0x7f08b6ab8e80>, <matplotlib.lines.Line2D object at 0x7f08b6ab8700>], 'caps': [<matplotlib.lines.Line2D object at 0x7f08b6ab8250>, <matplotlib.lines.Line2D object at 0x7f08b6ae9130>], 'boxes': [<matplotlib.lines.Line2D object at 0x7f08b6ab8670>], 'medians': [<matplotlib.lines.Line2D object at 0x7f08b6ae9490>], 'fliers': [], 'means': []}

red_square = dict(markerfacecolor='r', marker='s')
fig5, ax5 = plt.subplots()
ax5.set_title('Horizontal Boxes')
ax5.boxplot(data, vert=False, flierprops=red_square)

Out:

{'whiskers': [<matplotlib.lines.Line2D object at 0x7f08b78ca760>, <matplotlib.lines.Line2D object at 0x7f08b78caa90>], 'caps': [<matplotlib.lines.Line2D object at 0x7f08b78cadf0>, <matplotlib.lines.Line2D object at 0x7f08b78f5190>], 'boxes': [<matplotlib.lines.Line2D object at 0x7f08b78ca400>], 'medians': [<matplotlib.lines.Line2D object at 0x7f08b78f54f0>], 'fliers': [<matplotlib.lines.Line2D object at 0x7f08b78f5850>], 'means': []}

fig6, ax6 = plt.subplots()
ax6.set_title('Shorter Whisker Length')
ax6.boxplot(data, flierprops=red_square, vert=False, whis=0.75)

Out:

{'whiskers': [<matplotlib.lines.Line2D object at 0x7f08b6cb7850>, <matplotlib.lines.Line2D object at 0x7f08b6cb7b80>], 'caps': [<matplotlib.lines.Line2D object at 0x7f08b6cb7ee0>, <matplotlib.lines.Line2D object at 0x7f08b6cbb280>], 'boxes': [<matplotlib.lines.Line2D object at 0x7f08b6cb74f0>], 'medians': [<matplotlib.lines.Line2D object at 0x7f08b6cbb5e0>], 'fliers': [<matplotlib.lines.Line2D object at 0x7f08b6cbb940>], 'means': []}

Fake up some more data

spread = np.random.rand(50) * 100
center = np.ones(25) * 40
flier_high = np.random.rand(10) * 100 + 100
flier_low = np.random.rand(10) * -100
d2 = np.concatenate((spread, center, flier_high, flier_low))

Making a 2-D array only works if all the columns are the same length. If they are not, then use a list instead. This is actually more efficient because boxplot converts a 2-D array into a list of vectors internally anyway.

data = [data, d2, d2[::2]]
fig7, ax7 = plt.subplots()
ax7.set_title('Multiple Samples with Different sizes')
ax7.boxplot(data)

plt.show()

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References

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

import matplotlib
matplotlib.axes.Axes.boxplot
matplotlib.pyplot.boxplot

Out:

<function boxplot at 0x7f08bbb75b80>