Stacked area chart in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a basic stacked area chart code

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

Matplotlib

import matplotlib.pyplot as plt

labels = ['A', 'B', 'C']
data = [[1, 2, 3], [2, 3, 4], [3, 4, 5]]
plt.stackplot(range(3), *data, labels=labels)
plt.legend(loc='upper left')
plt.show()

A A line chart with three lines labeled A, B, and C

B A stacked area chart with three layers increasing from left to right, labeled A, B, and C

C A bar chart with three bars labeled A, B, and C

D A scatter plot with points labeled A, B, and C

💡 Hint

Stacked area charts fill areas between lines stacked on top of each other.

The plt.stackplot function creates a stacked area chart where each data series is stacked vertically. The labels appear in the legend.

❓ data_output

intermediate

Number of layers in stacked area chart

Given the data below used in a stacked area chart, how many layers will the chart have?

Matplotlib

data = [[5, 3, 6, 2], [1, 4, 2, 3], [3, 2, 1, 5], [4, 1, 3, 4]]

A 3

B 2

C 4

D 5

💡 Hint

Each inner list represents one layer in the stacked area chart.

The data list has 4 inner lists, so the stacked area chart will have 4 layers stacked on top of each other.

🔧 Debug

advanced

Identify the error in stacked area chart code

What error will this code raise when trying to plot a stacked area chart?

Matplotlib

import matplotlib.pyplot as plt

x = [0, 1, 2]
y = [[1, 2], [3, 4], [5, 6]]
plt.stackplot(x, *y)
plt.show()

A ValueError: x and y must have same length

B IndexError: list index out of range

C TypeError: unhashable type: 'list'

D No error, chart displays correctly

💡 Hint

Check if x and y data lengths match for plotting.

The x list has length 3, but y is a list of 3 lists each of length 2, so y's shape does not match x's length, causing a ValueError.

❓ visualization

advanced

Effect of alpha parameter in stacked area chart

What visual effect does setting alpha=0.5 have on a stacked area chart in matplotlib?

Matplotlib

import matplotlib.pyplot as plt

x = [0, 1, 2, 3]
y = [[1, 2, 3, 4], [2, 1, 2, 1]]
plt.stackplot(x, *y, alpha=0.5)
plt.show()

A The stacked areas become semi-transparent, allowing background or overlapping colors to show through

B The stacked areas become fully opaque and brighter

C The stacked areas disappear completely

D The stacked areas change to dashed outlines without fill

💡 Hint

Alpha controls transparency in matplotlib plots.

Setting alpha to 0.5 makes the colors half transparent, so you can see layers beneath or background grid lines.

🧠 Conceptual

expert

Interpreting stacked area chart data trends

In a stacked area chart showing sales of three products over time, if the total height of the stack increases but the bottom layer's area stays the same, what does this indicate?

A Sales of the bottom product increased and others decreased

B Sales of all products increased equally

C Sales of the bottom product decreased while others increased

D Sales of the bottom product stayed constant while sales of other products increased

💡 Hint

The bottom layer's area represents its absolute value over time.

If the bottom layer's area stays the same, its sales did not change. The total stack height increasing means other products' sales increased.