How to plot a nested pie chart in Matplotlib?

A nested pie chart displays hierarchical data with an outer ring representing main categories and an inner ring showing subcategories. Matplotlib's pie() function can create concentric pie charts by adjusting the radius and width parameters.

Creating a Basic Nested Pie Chart

Here's how to create a nested pie chart with outer and inner rings ?

import matplotlib.pyplot as plt
import numpy as np

# Set figure size
plt.rcParams["figure.figsize"] = [8, 6]
plt.rcParams["figure.autolayout"] = True

# Create figure and subplot
fig, ax = plt.subplots()

# Define data and styling
size = 0.3
vals = np.array([[60., 32.], [37., 40.], [29., 10.]])
cmap = plt.get_cmap("tab20c")
outer_colors = cmap(np.arange(3)*4)
inner_colors = cmap([1, 2, 5, 6, 9, 10])

# Create outer pie chart
ax.pie(vals.sum(axis=1), radius=1, colors=outer_colors,
       wedgeprops=dict(width=size, edgecolor='w'))

# Create inner pie chart
ax.pie(vals.flatten(), radius=1-size, colors=inner_colors,
       wedgeprops=dict(width=size, edgecolor='w'))

plt.title('Nested Pie Chart')
plt.show()

Enhanced Nested Pie Chart with Labels

Adding labels and percentages makes the chart more informative ?

import matplotlib.pyplot as plt
import numpy as np

fig, ax = plt.subplots(figsize=(10, 8))

# Data for nested pie chart
categories = ['Category A', 'Category B', 'Category C']
subcategories = ['A1', 'A2', 'B1', 'B2', 'C1', 'C2']
vals = np.array([[45, 25], [30, 35], [20, 15]])

# Colors
outer_colors = ['#ff9999', '#66b3ff', '#99ff99']
inner_colors = ['#ffcccc', '#ff6666', '#cce6ff', '#3399ff', 
                '#ccffcc', '#66ff66']

# Outer ring (main categories)
wedges1, texts1, autotexts1 = ax.pie(vals.sum(axis=1), 
                                      radius=1, 
                                      colors=outer_colors,
                                      labels=categories,
                                      autopct='%1.1f%%',
                                      wedgeprops=dict(width=0.4, edgecolor='white'))

# Inner ring (subcategories)  
wedges2, texts2, autotexts2 = ax.pie(vals.flatten(), 
                                      radius=0.6, 
                                      colors=inner_colors,
                                      labels=subcategories,
                                      autopct='%1.1f%%',
                                      wedgeprops=dict(width=0.4, edgecolor='white'))

plt.title('Enhanced Nested Pie Chart with Labels', fontsize=16, pad=20)
plt.show()

Key Parameters

Conclusion

Nested pie charts are created by plotting two pie charts with different radii and widths. The outer ring represents main categories while the inner ring shows subcategories, making hierarchical data visualization clear and intuitive.