Dumbbell charts in Matplotlib

Introduction

Dumbbell charts help compare two related values side by side for each item. They make it easy to see differences and changes.

Comparing sales numbers for two years for different products.

Showing before and after results of a test for multiple students.

Visualizing changes in population between two time points for cities.

Comparing two measurements like temperature in morning and evening for several days.

Syntax

Matplotlib

import matplotlib.pyplot as plt

# Data
categories = ['A', 'B', 'C']
value1 = [10, 20, 15]
value2 = [15, 18, 20]

# Plot
plt.hlines(y=categories, xmin=value1, xmax=value2, color='gray')
plt.scatter(value1, categories, color='blue', label='Value 1')
plt.scatter(value2, categories, color='red', label='Value 2')

plt.legend()
plt.show()

Use hlines to draw horizontal lines between two values.

Use scatter to plot points at each value.

Examples

Simple dumbbell chart with two categories and two values each.

Matplotlib

import matplotlib.pyplot as plt

categories = ['X', 'Y']
val1 = [5, 7]
val2 = [8, 6]

plt.hlines(y=categories, xmin=val1, xmax=val2, color='black')
plt.scatter(val1, categories, color='green')
plt.scatter(val2, categories, color='orange')
plt.show()

Dumbbell chart with bigger points and a title.

Matplotlib

import matplotlib.pyplot as plt

categories = ['Item1', 'Item2', 'Item3']
val1 = [12, 9, 14]
val2 = [15, 11, 13]

plt.hlines(categories, val1, val2, color='purple', linewidth=2)
plt.scatter(val1, categories, color='purple', s=100)
plt.scatter(val2, categories, color='orange', s=100)
plt.title('Dumbbell Chart Example')
plt.show()

Sample Program

This program creates a dumbbell chart comparing sales for 2023 and 2024 for four products. Lines connect the two sales values for each product, and points show exact sales.

Matplotlib

import matplotlib.pyplot as plt

# Categories and two sets of values
categories = ['Product A', 'Product B', 'Product C', 'Product D']
sales_2023 = [200, 340, 300, 280]
sales_2024 = [220, 310, 330, 290]

# Draw lines between sales of 2023 and 2024
plt.hlines(y=categories, xmin=sales_2023, xmax=sales_2024, color='gray', linewidth=2)

# Plot sales points for each year
plt.scatter(sales_2023, categories, color='blue', label='2023 Sales', s=100)
plt.scatter(sales_2024, categories, color='red', label='2024 Sales', s=100)

# Add labels and legend
plt.xlabel('Sales')
plt.title('Sales Comparison Dumbbell Chart')
plt.legend()

plt.show()

Important Notes

Make sure your two value lists have the same length as the categories list.

You can customize colors and sizes of points to improve clarity.

Dumbbell charts work best when comparing exactly two values per category.

Summary

Dumbbell charts show two values side by side for easy comparison.

Use horizontal lines and scatter points to build the chart in matplotlib.

They help visualize changes or differences clearly.