Nested subplots with subfigures in Matplotlib - Mini Project: Build & Apply

Nested subplots with subfigures

📖 Scenario: You are preparing a report with multiple charts. You want to organize these charts neatly using nested subplots and subfigures in matplotlib. This will help you compare different data groups side by side.

🎯 Goal: Create a figure with two subfigures arranged horizontally. Each subfigure contains two vertically stacked subplots showing simple line plots.

📋 What You'll Learn

Create a figure with matplotlib.pyplot.figure() using constrained_layout=True

Create two subfigures arranged in one row and two columns using fig.subfigures()

Each subfigure should have two subplots arranged vertically using subfig.subplots()

Plot simple line plots in each subplot with different data

Display the final figure with plt.show()

💡 Why This Matters

🌍 Real World

Nested subplots with subfigures help organize multiple related charts in reports or presentations, making it easier to compare data groups side by side.

💼 Career

Data scientists and analysts often create complex visualizations to communicate insights clearly. Knowing how to use nested subplots and subfigures is valuable for producing professional-quality charts.

1

Create the main figure with constrained layout

Create a figure called fig using plt.figure() with constrained_layout=True.

Matplotlib

import matplotlib.pyplot as plt

# Create the main figure with constrained_layout=True
# Your code here

Hint

Use plt.figure(constrained_layout=True) to create the figure.

2

Add two subfigures side by side

Using the figure fig, create two subfigures called subfig1 and subfig2 arranged in 1 row and 2 columns using fig.subfigures(1, 2).

Matplotlib

import matplotlib.pyplot as plt

fig = plt.figure(constrained_layout=True)

# Create two subfigures side by side
# Your code here

Hint

Use fig.subfigures(1, 2) to create two subfigures in one row and two columns.

3

Create two vertical subplots in each subfigure and plot lines

For each subfigure subfig1 and subfig2, create two subplots arranged vertically using subfig.subplots(2, 1). Then plot simple line plots on each subplot using ax.plot() with these data: for subfig1 use [1, 2, 3] and [3, 2, 1], for subfig2 use [4, 5, 6] and [6, 5, 4].

Matplotlib

import matplotlib.pyplot as plt

fig = plt.figure(constrained_layout=True)
subfig1, subfig2 = fig.subfigures(1, 2)

# Create two vertical subplots in each subfigure
# Plot simple line plots on each subplot
# Your code here

Hint

Use subfig.subplots(2, 1) to create two vertical subplots. Use ax.plot() to draw lines.

4

Display the figure with nested subplots

Use plt.show() to display the figure with the nested subplots and subfigures.

Matplotlib

import matplotlib.pyplot as plt

fig = plt.figure(constrained_layout=True)
subfig1, subfig2 = fig.subfigures(1, 2)

axs1 = subfig1.subplots(2, 1)
axs1[0].plot([1, 2, 3])
axs1[1].plot([3, 2, 1])

axs2 = subfig2.subplots(2, 1)
axs2[0].plot([4, 5, 6])
axs2[1].plot([6, 5, 4])

# Display the figure
# Your code here

Hint

Call plt.show() to display the figure.

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