Small multiples (facet grid) in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple facet grid plot

What will be the shape of the figure created by this code using matplotlib's subplots for small multiples?

Matplotlib

import matplotlib.pyplot as plt
import numpy as np

x = np.linspace(0, 10, 100)
fig, axs = plt.subplots(2, 3)
for i, ax in enumerate(axs.flatten()):
    ax.plot(x, np.sin(x + i))
plt.close(fig)
print(fig.get_size_inches())

A [12.0 8.0]

B [18.0 12.0]

C [6.0 4.0]

D [8.0 6.0]

💡 Hint

The default figsize for plt.subplots is (6, 4) inches.

By default, plt.subplots creates a figure of size 6 inches wide and 4 inches tall unless specified otherwise.

❓ data_output

intermediate

Number of subplots created

How many subplots will be created by this code snippet?

Matplotlib

import matplotlib.pyplot as plt
fig, axs = plt.subplots(3, 4)
print(len(axs.flatten()))

A 7

B 12

C 3

D 4

💡 Hint

Count rows times columns.

3 rows times 4 columns equals 12 subplots.

❓ visualization

advanced

Identify the correct facet grid layout

Which option shows the correct arrangement of subplots for this code?

Matplotlib

import matplotlib.pyplot as plt
import numpy as np
x = np.linspace(0, 2 * np.pi, 100)
fig, axs = plt.subplots(2, 2)
for i, ax in enumerate(axs.flatten()):
    ax.plot(x, np.sin(x + i))
plt.close(fig)
# The question is about the layout of subplots in a 2x2 grid.

A Four plots arranged in 2 rows and 2 columns

B Four plots arranged in 1 row and 4 columns

C Two plots arranged in 2 rows and 1 column

D Three plots arranged in 3 rows and 1 column

💡 Hint

Check the arguments of plt.subplots(2, 2).

plt.subplots(2, 2) creates a grid with 2 rows and 2 columns, so 4 plots arranged accordingly.

🔧 Debug

advanced

Error in facet grid subplot indexing

What error will this code raise?

Matplotlib

import matplotlib.pyplot as plt
fig, axs = plt.subplots(2, 2)
axs[2].plot([1, 2, 3], [4, 5, 6])

A IndexError: index 2 is out of bounds for axis 0 with size 2

B AttributeError: 'AxesSubplot' object has no attribute 'plot'

C TypeError: 'AxesSubplot' object is not subscriptable

D No error, plot will be created

💡 Hint

axs is a 2D array of shape (2, 2).

axs is a 2x2 array, so axs[2] is out of bounds. Indexing must be two-dimensional or flattened first.

🚀 Application

expert

Creating a facet grid with shared axes

Which code snippet correctly creates a 3x2 facet grid with shared x and y axes using matplotlib?

A fig, axs = plt.subplots(3, 2, sharex=False, sharey=True)

B fig, axs = plt.subplots(3, 2, sharex=True, sharey=False)

C fig, axs = plt.subplots(2, 3, sharex=True, sharey=True)

D fig, axs = plt.subplots(3, 2, sharex=True, sharey=True)

💡 Hint

Check the order of rows and columns and the sharex/sharey parameters.

plt.subplots(3, 2, sharex=True, sharey=True) creates 3 rows and 2 columns with shared axes.

Practice

1. What is the main purpose of using small multiples (facet grid) in matplotlib?

easy

A. To display multiple related charts side by side for easy comparison

B. To create a single large plot with multiple lines

C. To animate a plot over time

D. To change the color scheme of a plot

Solution

1. Step 1: Understand the concept of small multiples

   Small multiples are multiple small charts arranged in a grid to compare different groups or categories easily.

2. Step 2: Identify the purpose in matplotlib

   Matplotlib uses small multiples to show many charts side by side, making it easier to compare data visually.

3. Final Answer:

   To display multiple related charts side by side for easy comparison -> Option A

4. Quick Check:

   Small multiples = multiple charts side by side [OK]

Hint: Small multiples = many small charts for comparison [OK]

Common Mistakes:

• Confusing small multiples with animations
• Thinking it changes colors only
• Assuming it creates one big plot

2. Which of the following is the correct way to create a 2x2 grid of subplots in matplotlib?

easy

A. fig, axes = plt.subplots(4)

B. fig, axes = plt.subplots(1, 4)

C. fig, axes = plt.subplots(2, 2)

D. fig, axes = plt.subplots(2)

Solution

1. Step 1: Recall plt.subplots() syntax

   plt.subplots(rows, columns) creates a grid of subplots with given rows and columns.

2. Step 2: Match the grid size

   To create a 2x2 grid, use plt.subplots(2, 2).

3. Final Answer:

   fig, axes = plt.subplots(2, 2) -> Option C

4. Quick Check:

   plt.subplots(2, 2) = 2 rows and 2 columns [OK]

Hint: Use plt.subplots(rows, columns) for grid size [OK]

Common Mistakes:

• Using single number for grid shape
• Confusing rows and columns
• Missing one dimension in arguments

3. What will be the output of this code snippet?

import matplotlib.pyplot as plt
fig, axes = plt.subplots(1, 3)
data = [1, 2, 3]
for i, ax in enumerate(axes):
    ax.plot([data[i]] * 3)
plt.show()

medium

A. Three line plots each with three points of the same value 1, 2, and 3 respectively

B. A single plot with three lines of values 1, 2, and 3

C. Error because axes is not iterable

D. Three scatter plots with points 1, 2, and 3

Solution

1. Step 1: Understand plt.subplots(1, 3)

   This creates 1 row and 3 columns of subplots, so axes is an array of 3 axes objects.

2. Step 2: Loop plots each subplot

   For each axis, it plots a line with three points all equal to data[i] (1, then 2, then 3).

3. Final Answer:

   Three line plots each with three points of the same value 1, 2, and 3 respectively -> Option A

4. Quick Check:

   Loop over axes plots lines with repeated values [OK]

Hint: Loop over axes to plot each subplot separately [OK]

Common Mistakes:

• Thinking axes is a single plot
• Assuming error due to axes type
• Confusing line plot with scatter plot

4. Identify the error in this code for creating a 2x2 grid of plots:

fig, axes = plt.subplots(2, 2)
for i in range(4):
    axes[i].plot([1, 2, 3])
plt.show()

medium

A. The plot data list is invalid

B. plt.subplots(2, 2) creates only 2 plots, not 4

C. plt.show() is missing

D. axes is a 2D array, so axes[i] indexing causes an error

Solution

1. Step 1: Understand axes shape from plt.subplots(2, 2)

   axes is a 2x2 numpy array of Axes objects, not a flat list.

2. Step 2: Identify indexing error

   axes[i] tries to index a 2D array with one index, causing an error. Correct is axes[row, col] or flatten axes first.

3. Final Answer:

   axes is a 2D array, so axes[i] indexing causes an error -> Option D

4. Quick Check:

   2D axes need two indices or flatten before looping [OK]

Hint: 2D axes need two indices or flatten before indexing [OK]

Common Mistakes:

• Assuming axes is 1D array
• Ignoring error from wrong indexing
• Thinking plt.show() is missing

5. You have a dataset with sales data for 3 regions. How would you create a 1-row, 3-column grid of plots showing sales trends for each region separately using matplotlib?

hard

A. Use plt.plot() three times without subplots

B. Use plt.subplots(1, 3), loop over axes, and plot each region's data on each subplot

C. Use plt.subplots(3, 1) and plot all regions on each subplot

D. Use plt.subplots(1, 1) and plot all regions on the same plot

Solution

1. Step 1: Create a 1x3 grid for three regions

   Use plt.subplots(1, 3) to create one row and three columns of plots.

2. Step 2: Loop over axes and plot each region's data

   Loop through each axis and plot the sales data for each region separately to compare trends side by side.

3. Final Answer:

   Use plt.subplots(1, 3), loop over axes, and plot each region's data on each subplot -> Option B

4. Quick Check:

   One row, three columns, loop to plot each region [OK]

Hint: Create grid then loop axes to plot groups separately [OK]

Common Mistakes:

• Plotting all data on one plot
• Using wrong grid shape
• Not looping over axes