Why Nested subplots with subfigures in Matplotlib? - Purpose & Use Cases

The Big Idea

What if you could arrange dozens of charts perfectly with just a few lines of code?

The Scenario

Imagine you have a big report with many charts. You want to show groups of related charts together, like a family photo album. Doing this by hand means creating each chart separately and then trying to arrange them perfectly on a page.

The Problem

Manually placing each chart is slow and tricky. You might spend hours adjusting sizes and positions. It's easy to make mistakes, like overlapping charts or uneven spacing. This wastes time and makes your report look messy.

The Solution

Nested subplots with subfigures let you organize charts in groups automatically. You create a main figure, then add smaller figures inside it, each with its own grid of charts. This keeps everything neat and aligned without extra effort.

Before vs After

✗ Before

fig, ax1 = plt.subplots()
ax1.plot(data1)
fig2, ax2 = plt.subplots()
ax2.plot(data2)
# Manually combine images later

✓ After

fig = plt.figure()
subfigs = fig.subfigures(2, 1)
ax1 = subfigs[0].subplots()
ax1.plot(data1)
ax2 = subfigs[1].subplots()
ax2.plot(data2)

What It Enables

You can create complex, well-organized multi-chart layouts easily, making your data stories clearer and more professional.

Real Life Example

A data analyst prepares a sales report with separate sections for each region. Using nested subplots with subfigures, they group charts by region, so managers quickly see trends without confusion.

Key Takeaways

Manual chart arrangement is slow and error-prone.

Nested subplots with subfigures automate neat grouping.

This makes multi-chart reports clear and easy to create.

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