matplotlib Plotting Cookbook

Plotting back-to-back bar charts

A simple but useful trick is to display two bar charts back-to-back at the same time. Think of an age pyramid of a population, showing the number of people within different age ranges. On the left side, we show the male population, while on the right we show the female population.

How to do it...

The idea is to have two bar charts, using a simple trick, that is, the length/height of one bar can be negative!

import numpy as np
import matplotlib.pyplot as plt

women_pop = np.array([5., 30., 45., 22.])
men_pop     = np.array( [5., 25., 50., 20.])
X = np.arange(4)

plt.barh(X, women_pop, color = 'r')
plt.barh(X, -men_pop, color = 'b')
plt.show()

The preceding script will produce the following graph:

How it works...

The bar chart ...