Nested subplots with subfigures in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of nested subplots with subfigures

What will be the output of the following code that creates nested subplots using subfigures in matplotlib?

Matplotlib

import matplotlib.pyplot as plt
import numpy as np

x = np.linspace(0, 10, 100)

fig = plt.figure(constrained_layout=True)
subfigs = fig.subfigures(1, 2)

ax1 = subfigs[0].subplots(2, 1)
ax1[0].plot(x, np.sin(x))
ax1[1].plot(x, np.cos(x))

ax2 = subfigs[1].subplots(1, 2)
ax2[0].plot(x, np.tan(x))
ax2[1].plot(x, np.exp(-x))

plt.show()

A A figure with two subfigures stacked vertically; each subfigure contains two plots side by side.

B A figure with two subfigures side by side; left subfigure has two rows of plots (sin and cos), right subfigure has two columns of plots (tan and exp decay).

C A single figure with four plots arranged in a 2x2 grid showing sin, cos, tan, and exp decay.

D An error occurs because subfigures cannot be nested inside a figure.

💡 Hint

Think about how subfigures split the main figure and how subplots inside each subfigure arrange axes.

The code creates a main figure split into two subfigures horizontally. The left subfigure has two rows of plots (sin and cos), and the right subfigure has two columns of plots (tan and exp decay). This matches option B.

❓ data_output

intermediate

Number of axes in nested subplots with subfigures

How many total axes (individual plots) are created by the following code?

Matplotlib

import matplotlib.pyplot as plt

fig = plt.figure()
subfigs = fig.subfigures(2, 1)

ax_top = subfigs[0].subplots(1, 3)
ax_bottom = subfigs[1].subplots(2, 2)

print(len(ax_top) + ax_bottom.size)

A 7

B 6

C 8

D 5

💡 Hint

Count the number of axes in each subfigure and add them.

The top subfigure has 1 row and 3 columns → 3 axes. The bottom subfigure has 2 rows and 2 columns → 4 axes. Total axes = 3 + 4 = 7. However, ax_bottom.size returns 4, and len(ax_top) returns 3, so the print outputs 7.

🔧 Debug

advanced

Identify the error in nested subfigures code

What error will this code raise?

Matplotlib

import matplotlib.pyplot as plt

fig = plt.figure()
subfigs = fig.subfigures(1, 2)

ax = subfigs.subplots(2, 2)

plt.show()

A AttributeError: 'SubFigure' object has no attribute 'subplots'

B AttributeError: 'numpy.ndarray' object has no attribute 'subfigures'

C TypeError: subfigures() missing 1 required positional argument

D AttributeError: 'numpy.ndarray' object has no attribute 'subplots'

💡 Hint

Check the type of subfigs and what methods it supports.

fig.subfigures(1, 2) returns a numpy array of SubFigure objects. Calling subfigs.subplots(2, 2) tries to call subplots on a numpy array, which does not have that method. This causes an AttributeError.

❓ visualization

advanced

Visual layout of nested subplots with subfigures

Which option best describes the layout of the figure created by this code?

Matplotlib

import matplotlib.pyplot as plt

fig = plt.figure(constrained_layout=True)
subfigs = fig.subfigures(2, 1)

ax1 = subfigs[0].subplots(1, 2)
ax2 = subfigs[1].subplots(3, 1)

plt.show()

A One figure with five plots arranged in a 3x2 grid.

B Two subfigures side by side; left subfigure has two plots stacked vertically, right subfigure has three plots side by side.

C Two subfigures stacked vertically; top subfigure has two plots side by side, bottom subfigure has three plots stacked vertically.

D A single subplot with five lines plotted.

💡 Hint

Look at the subfigures(2, 1) call and how subplots are arranged inside each subfigure.

The main figure is split into two subfigures stacked vertically. The top subfigure has 1 row and 2 columns (two plots side by side). The bottom subfigure has 3 rows and 1 column (three plots stacked vertically). This matches option C.

🚀 Application

expert

Creating a complex nested subplot layout with subfigures

You want to create a figure with three subfigures arranged horizontally. The first subfigure has a 2x1 grid of plots, the second subfigure has a single plot, and the third subfigure has a 2x2 grid of plots. Which code snippet correctly creates this layout?

A

fig = plt.figure()
subfigs = fig.subfigures(1, 3)
ax1 = subfigs[0].subplots(2, 1)
ax2 = subfigs[1].subplots(1, 1)
ax3 = subfigs[2].subplots(2, 2)

B

fig = plt.figure()
subfigs = fig.subfigures(3, 1)
ax1 = subfigs[0].subplots(1, 2)
ax2 = subfigs[1].subplots(1, 1)
ax3 = subfigs[2].subplots(2, 2)

C

fig = plt.figure()
subfigs = fig.subfigures(1, 3)
ax1 = subfigs[0].subplots(1, 2)
ax2 = subfigs[1].subplots(1, 1)
ax3 = subfigs[2].subplots(2, 2)

D

fig = plt.figure()
subfigs = fig.subfigures(1, 3)
ax1 = subfigs[0].subplots(2, 1)
ax2 = subfigs[1].subplots(2, 2)
ax3 = subfigs[2].subplots(1, 1)

💡 Hint

Remember the first argument to subfigures is rows, second is columns. Match the grids inside each subfigure carefully.

Option A correctly creates one row and three columns of subfigures. The first subfigure has 2 rows and 1 column, the second has 1 plot, and the third has 2 rows and 2 columns. Other options either swap rows and columns or assign wrong grids.

Practice

1. What is the main purpose of using fig.subfigures() in matplotlib?

easy

A. To add a single plot to a figure

B. To create large groups inside a figure that can hold their own smaller plots

C. To change the color of a plot

D. To save a figure as an image file

Solution

1. Step 1: Understand the role of fig.subfigures()

   This method creates subfigures, which are large groups inside a main figure.

2. Step 2: Recognize the use of subfigures

   Each subfigure can contain its own grid of smaller plots, helping organize complex layouts.

3. Final Answer:

   To create large groups inside a figure that can hold their own smaller plots -> Option B

4. Quick Check:

   Subfigures = large groups inside figure [OK]

Hint: Subfigures group plots inside a figure [OK]

Common Mistakes:

• Thinking subfigures add only one plot
• Confusing subfigures with saving figures
• Assuming subfigures change plot colors

2. Which of the following is the correct way to create two subfigures side by side in matplotlib?

easy

A. fig.subplots(1, 2)

B. fig.subfigures(2, 1)

C. fig.subfigures(1, 2)

D. fig.subfigures(2, 2)

Solution

1. Step 1: Understand subfigures layout parameters

   The parameters (rows, columns) define the grid of subfigures. For side by side, use 1 row and 2 columns.

2. Step 2: Match parameters to options

   fig.subfigures(1, 2) uses fig.subfigures(1, 2), which creates 1 row and 2 columns, placing subfigures side by side.

3. Final Answer:

   fig.subfigures(1, 2) -> Option C

4. Quick Check:

   Side by side = 1 row, 2 columns [OK]

Hint: Rows first, columns second in subfigures() [OK]

Common Mistakes:

• Swapping rows and columns
• Using subplots() instead of subfigures()
• Choosing more rows than needed

3. What will be the output shape of the axes array when running this code?

fig = plt.figure()
subfigs = fig.subfigures(2, 1)
ax1 = subfigs[0].subplots(1, 3)
ax2 = subfigs[1].subplots(2, 2)
print(ax1.shape, ax2.shape)

medium

A. (1, 3) (4,)

B. (3,) (4,)

C. (3,) (2, 2)

D. (1, 3) (2, 2)

Solution

1. Step 1: Analyze subfigures and their subplot grids

   First subfigure has 1 row and 3 columns, so ax1 shape is (1, 3). Second subfigure has 2 rows and 2 columns, so ax2 shape is (2, 2).

2. Step 2: Confirm shapes printed

   Printing ax1.shape and ax2.shape outputs (1, 3) and (2, 2) respectively.

3. Final Answer:

   (1, 3) (2, 2) -> Option D

4. Quick Check:

   Subplots shape = (rows, columns) [OK]

Hint: Shape matches (rows, columns) in subplots() [OK]

Common Mistakes:

• Confusing flat arrays with 2D arrays
• Mixing up rows and columns
• Assuming subfigures affect shape differently

4. Identify the error in this code snippet for creating nested subplots with subfigures:

fig = plt.figure()
subfigs = fig.subfigures(1, 2)
ax = subfigs.subplots(2, 2)

medium

A. subfigs.subplots() should be called on each subfigure, not on the list

B. fig.subfigures() requires 3 arguments, missing one

C. subfigs is a list, so subfigs.subplots() is invalid

D. subfigures cannot have nested subplots

Solution

1. Step 1: Understand the type of subfigs

   fig.subfigures(1, 2) returns a list or array of subfigure objects, not a single subfigure.

2. Step 2: Correct method call for subplots

   We must call subplots() on each individual subfigure, not on the entire list subfigs.

3. Final Answer:

   subfigs.subplots() should be called on each subfigure, not on the list -> Option A

4. Quick Check:

   Call subplots() on single subfigure [OK]

Hint: Call subplots() on one subfigure, not list [OK]

Common Mistakes:

• Calling subplots() on the list of subfigures
• Assuming subfigures() needs 3 args
• Thinking subfigures can't have subplots

5. You want to create a figure with 2 subfigures stacked vertically. The top subfigure should have a 2x2 grid of plots, and the bottom subfigure a single plot. Which code correctly achieves this?

hard

A. fig = plt.figure()
subfigs = fig.subfigures(2, 1)
axs_top = subfigs[0].subplots(2, 2)
axs_bottom = subfigs[1].subplots(1, 1)

B. fig = plt.figure()
subfigs = fig.subfigures(1, 2)
axs_top = subfigs[0].subplots(2, 2)
axs_bottom = subfigs[1].subplots(1, 1)

C. fig = plt.figure()
subfigs = fig.subfigures(2, 1)
axs_top = subfigs.subplots(2, 2)
axs_bottom = subfigs.subplots(1, 1)

D. fig = plt.figure()
subfigs = fig.subfigures(1, 2)
axs_top = subfigs.subplots(2, 2)
axs_bottom = subfigs.subplots(1, 1)

Solution

1. Step 1: Set subfigures layout vertically

   Two subfigures stacked vertically means 2 rows and 1 column, so fig.subfigures(2, 1).

2. Step 2: Create subplots inside each subfigure

   Top subfigure gets a 2x2 grid, bottom subfigure gets a single plot (1x1). Call subplots() on each subfigure individually.

3. Final Answer:

   fig = plt.figure() subfigs = fig.subfigures(2, 1) axs_top = subfigs[0].subplots(2, 2) axs_bottom = subfigs[1].subplots(1, 1) -> Option A

4. Quick Check:

   Vertical stack = (2,1), call subplots() on each subfigure [OK]

Hint: Vertical stack = (2,1), subplots() on each subfigure [OK]

Common Mistakes:

• Using (1,2) for vertical stacking
• Calling subplots() on the list of subfigures
• Not matching subplot grids to subfigures