Multiple images in subplot grid in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of subplot grid with 2 images

What will be the output of this code that plots two images side by side using matplotlib subplots?

Matplotlib

import matplotlib.pyplot as plt
import numpy as np

img1 = np.ones((5,5))
img2 = np.zeros((5,5))

fig, axs = plt.subplots(1, 2)
axs[0].imshow(img1, cmap='gray')
axs[1].imshow(img2, cmap='gray')
plt.show()

A A figure with two images: left is a white square, right is a black square.

B An error because axs is not iterable.

C A single image showing a gradient from black to white.

D A figure with two images stacked vertically.

💡 Hint

Check how subplots are arranged and how images are assigned to axes.

The code creates a 1x2 grid of subplots. The first subplot shows a white 5x5 image (all ones), the second shows a black 5x5 image (all zeros).

❓ data_output

intermediate

Number of axes in a 3x3 subplot grid

How many axes objects are created when you run this code?

Matplotlib

import matplotlib.pyplot as plt
fig, axs = plt.subplots(3, 3)
print(len(axs.flatten()))

A 1

B 3

C 9

D 6

💡 Hint

Count rows times columns in the subplot grid.

A 3x3 grid creates 9 axes objects. Flattening axs gives a list of all 9 axes.

❓ visualization

advanced

Identify the subplot layout from the image

Given a figure with 4 images arranged in a 2x2 grid, which code snippet correctly creates this layout?

A

fig, axs = plt.subplots(1, 4)
for i, ax in enumerate(axs):
    ax.imshow(np.full((3,3), i))

B

fig, axs = plt.subplots(2, 2)
for i, ax in enumerate(axs.flatten()):
    ax.imshow(np.full((3,3), i))

C

fig, axs = plt.subplots(4, 1)
for i, ax in enumerate(axs):
    ax.imshow(np.full((3,3), i))

D

fig, axs = plt.subplots(3, 3)
for i, ax in enumerate(axs.flatten()[:4]):
    ax.imshow(np.full((3,3), i))

💡 Hint

Check the shape of the subplot grid and how images are assigned.

Option B creates a 2x2 grid and fills each subplot with a different image. Others create wrong grid shapes or use extra subplots.

🔧 Debug

advanced

Why does this subplot code raise an error?

This code raises an error. What is the cause?

Matplotlib

import matplotlib.pyplot as plt
fig, axs = plt.subplots(1, 1)
axs.imshow([[1, 2], [3, 4]])
plt.show()

A 'AxesSubplot' object has no attribute 'imshow'

B TypeError because axs is not an array but a single Axes object

C IndexError because axs is not subscriptable

D No error, the code runs fine

💡 Hint

Check the type of axs when subplots(1,1) is used.

When subplots(1,1) is called, axs is a single Axes object, not an array. It has imshow method, so no error occurs.

🚀 Application

expert

Arrange 6 images in a 2x3 grid with shared axes

You want to plot 6 images in a 2 rows by 3 columns grid using matplotlib. You want all subplots to share the same x and y axes to compare images easily. Which code snippet achieves this?

A

fig, axs = plt.subplots(2, 3, sharex=True, sharey=True)
for ax in axs.flatten():
    ax.imshow(np.random.rand(5,5))
plt.show()

B

fig, axs = plt.subplots(2, 3)
for ax in axs.flatten():
    ax.imshow(np.random.rand(5,5))
plt.show()

C

fig, axs = plt.subplots(6, 1, sharex=True, sharey=True)
for ax in axs:
    ax.imshow(np.random.rand(5,5))
plt.show()

D

fig, axs = plt.subplots(3, 2, sharex=True, sharey=True)
for ax in axs.flatten():
    ax.imshow(np.random.rand(5,5))
plt.show()

💡 Hint

Check the shape of the grid and the sharex/sharey parameters.

Option A creates a 2x3 grid with shared x and y axes, matching the requirement. Option A swaps rows and columns, A lacks shared axes, C creates a 6x1 grid.