Dumbbell charts in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Dumbbell Chart Code

What will be the output of this Python code that creates a dumbbell chart using matplotlib?

Matplotlib

import matplotlib.pyplot as plt

categories = ['A', 'B', 'C']
values_1 = [10, 20, 30]
values_2 = [15, 18, 35]

plt.hlines(y=categories, xmin=values_1, xmax=values_2, color='gray')
plt.scatter(values_1, categories, color='blue', label='Start')
plt.scatter(values_2, categories, color='red', label='End')
plt.legend()
plt.show()

A A scatter plot with points only for values_1 and values_2 without connecting lines

B A vertical bar chart with three bars for categories A, B, and C

C A horizontal dumbbell chart with three lines connecting blue and red dots for categories A, B, and C

D A line plot connecting values_1 and values_2 points in sequence

💡 Hint

Look at how hlines and scatter are used to connect points horizontally.

The code uses horizontal lines (hlines) to connect two sets of values for each category, then plots scatter points at the start and end values, creating a dumbbell chart.

❓ data_output

intermediate

Number of Lines in Dumbbell Chart

Given the following data, how many horizontal lines will be drawn in the dumbbell chart code below?

Matplotlib

categories = ['X', 'Y', 'Z', 'W']
values_1 = [5, 10, 15, 20]
values_2 = [7, 12, 18, 25]

# Lines drawn using plt.hlines(y=categories, xmin=values_1, xmax=values_2)

A 4

B 3

C 2

D 5

💡 Hint

Each category corresponds to one horizontal line.

There are 4 categories, so 4 horizontal lines will be drawn connecting the start and end values for each category.

❓ visualization

advanced

Identify the Dumbbell Chart Visualization

Which option best describes the visual output of this dumbbell chart code snippet?

Matplotlib

import matplotlib.pyplot as plt

labels = ['Group1', 'Group2']
start = [100, 150]
end = [120, 130]

plt.hlines(y=labels, xmin=start, xmax=end, color='green', linewidth=4)
plt.scatter(start, labels, color='orange', s=100)
plt.scatter(end, labels, color='purple', s=100)
plt.show()

A Two horizontal thick green lines with orange dots on the left and purple dots on the right for each group

B A scatter plot with orange and purple dots randomly placed

C Two vertical green lines with orange and purple dots stacked vertically

D A bar chart with green bars and dots on top

💡 Hint

Check the use of hlines and scatter with horizontal y-axis labels.

The code draws horizontal thick green lines between start and end values for each group, with colored dots marking the ends, forming a dumbbell chart.

🔧 Debug

advanced

Error in Dumbbell Chart Code

What error will this dumbbell chart code produce when run?

Matplotlib

import matplotlib.pyplot as plt

categories = ['A', 'B', 'C']
values_1 = [10, 20]
values_2 = [15, 25, 30]

plt.hlines(y=categories, xmin=values_1, xmax=values_2, color='black')
plt.scatter(values_1, categories, color='blue')
plt.scatter(values_2, categories, color='red')
plt.show()

A No error, chart displays correctly

B TypeError because categories are strings

C IndexError from accessing out-of-range list elements

D ValueError due to mismatched lengths of y and xmin arrays

💡 Hint

Check if all input lists have the same length.

The y-axis categories list has length 3, but values_1 has length 2, causing a ValueError when plotting hlines.

🚀 Application

expert

Calculate Difference from Dumbbell Chart Data

Given the following data used in a dumbbell chart, what is the average difference between the two value sets?

Matplotlib

categories = ['P', 'Q', 'R', 'S']
values_1 = [50, 60, 70, 80]
values_2 = [55, 65, 75, 90]

differences = [v2 - v1 for v1, v2 in zip(values_1, values_2)]
avg_diff = sum(differences) / len(differences)
print(round(avg_diff, 2))

A 10.0

B 6.25

C 5.0

D 7.5

💡 Hint

Calculate each difference, then average them.

Differences are [5, 5, 5, 10]. Their average is (5+5+5+10)/4 = 6.25. But careful: sum is 25, average is 6.25. The code prints 6.25, so option B is correct.