Stacked bar charts in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a basic stacked bar chart code

What will be the output of this code snippet that creates a stacked bar chart using matplotlib?

Matplotlib

import matplotlib.pyplot as plt

labels = ['A', 'B', 'C']
values1 = [3, 5, 1]
values2 = [2, 3, 4]

plt.bar(labels, values1, label='Group 1')
plt.bar(labels, values2, bottom=values1, label='Group 2')
plt.legend()
plt.show()

A A bar chart with three bars labeled A, B, C, each bar split into two stacked segments representing Group 1 and Group 2 values.

B A line chart connecting points for Group 1 and Group 2 values over labels A, B, C.

C A bar chart with bars for Group 1 and Group 2 side by side for each label A, B, C.

D A scatter plot showing points for Group 1 and Group 2 values at labels A, B, C.

💡 Hint

Stacked bars use the 'bottom' parameter to stack one bar on top of another.

The code uses plt.bar twice with the same labels. The second bar uses 'bottom=values1' to stack on top of the first bars, creating a stacked bar chart.

❓ data_output

intermediate

Resulting heights of stacked bars

Given these data arrays for two groups, what is the total height of the stacked bars for each label after stacking?

Matplotlib

values1 = [4, 2, 7]
values2 = [1, 3, 2]
# Total height is values1 + values2 element-wise

A [1, 3, 2]

B [3, 5, 9]

C [4, 3, 7]

D [5, 5, 9]

💡 Hint

Add the values from both groups for each label.

The total height of each stacked bar is the sum of the corresponding values from values1 and values2.

🔧 Debug

advanced

Identify the error in this stacked bar chart code

What error will this code produce when run?

Matplotlib

import matplotlib.pyplot as plt
labels = ['X', 'Y']
values1 = [3, 4]
values2 = [2, 5, 1]
plt.bar(labels, values1, label='First')
plt.bar(labels, values2, bottom=values1, label='Second')
plt.legend()
plt.show()

A No error, the plot will display correctly

B TypeError because bottom parameter must be a single number

C ValueError due to mismatched lengths of values2 and labels

D IndexError because values1 is shorter than values2

💡 Hint

Check if the lengths of values arrays match the labels.

values2 has 3 elements but labels has 2, so matplotlib raises a ValueError about mismatched lengths.

❓ visualization

advanced

Interpreting a stacked bar chart visualization

You see a stacked bar chart with three bars labeled Jan, Feb, Mar. Each bar has two colors: blue on bottom and orange on top. The blue segments are 5, 3, 4 units tall respectively. The orange segments are 2, 6, 1 units tall respectively. What is the total height of the bar for February?

A 3 units

B 9 units

C 6 units

D 5 units

💡 Hint

Add the heights of the stacked segments for February.

February's total height is blue segment (3) plus orange segment (6) = 9 units.

🚀 Application

expert

Calculate percentage contribution in stacked bars

Given these data for three categories over two groups, calculate the percentage contribution of Group 2 to the total stacked bar height for category 'B'. Category labels: ['A', 'B', 'C'] Group 1 values: [10, 20, 30] Group 2 values: [5, 15, 10] What is the percentage contribution of Group 2 in category 'B'?

A 42.86%

B 60.00%

C 33.33%

D 75.00%

💡 Hint

Percentage = (Group 2 value / (Group 1 value + Group 2 value)) * 100

For category B, Group 1 is 20 and Group 2 is 15. Total is 35. Percentage = (15/35)*100 = 42.86%.