how to make a grouped boxplot graph in matplotlib

Question

I have three algorithms, A, B, and C. I've run them on different datasets and would like to graph their runtimes on each as a grouped boxplot in Python.

As a visual example of what I want, I made a terrible drawing, but hopefully it gets the point across.

boxplot graph drawing

If my data in python looks like this:

import numpy as np import random data = {} data['dataset1'] = {} data['dataset2'] = {} data['dataset3'] = {} n = 5 for k,v in data.iteritems(): upper = random.randint(0, 1000) v['A'] = np.random.uniform(0, upper, size=n) v['B'] = np.random.uniform(0, upper, size=n) v['C'] = np.random.uniform(0, upper, size=n)

How can I make my plot look like the picture I drew?

If you use boxplots regularly, take a look at github.com/matplotlib/matplotlib/pull/2643 which is adding a more flexible interface. — tacaswell
– tacaswell, Commented Dec 4, 2013 at 3:32

Joe Kington · Accepted Answer · 2013-12-04 01:36:38Z

18

It's easiest to do this with independent subplots:

import matplotlib.pyplot as plt import numpy as np import random data = {} data['dataset1'] = {} data['dataset2'] = {} data['dataset3'] = {} n = 500 for k,v in data.iteritems(): upper = random.randint(0, 1000) v['A'] = np.random.uniform(0, upper, size=n) v['B'] = np.random.uniform(0, upper, size=n) v['C'] = np.random.uniform(0, upper, size=n) fig, axes = plt.subplots(ncols=3, sharey=True) fig.subplots_adjust(wspace=0) for ax, name in zip(axes, ['dataset1', 'dataset2', 'dataset3']): ax.boxplot([data[name][item] for item in ['A', 'B', 'C']]) ax.set(xticklabels=['A', 'B', 'C'], xlabel=name) ax.margins(0.05) # Optional plt.show()

enter image description here

answered Dec 4, 2013 at 1:36

Joe Kington

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5 Comments

lollercoaster Over a year ago

perfectly what I wanted! thanks. always amazed how versatile matplotlib in python is.

Joe Kington Over a year ago

@lollercoaster - Happy to help! Your sketch and example data made your question very clear and easy to answer, for whatever it's worth. Excellent question!

Deditos Over a year ago

@JoeKington How did you get rid of the yticklabels on plots 2 and 3? They appear on all three plots for me, and if I remove them from one they disappear from all three because the yaxis is shared.

Joe Kington Over a year ago

@Deditos - Using subplots with sharey=True should automatically hide them, but if it's not for some reason, use plt.setp(ax2.get_yticklabels(), visible=False) (and repeat for ax3). What you're running into is a bit of a classic gotcha with shared axes. The plt.setp(..., visible=False) is a workaround so that they're still shown on the first axes, but not on the other shared ones.

Deditos Over a year ago

@JoeKington: It's probably because I'm using an old matplotlib version, but that manual setp command does the trick, thanks!

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