Axes creation with add_subplot in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output shape of the figure's axes array?

Consider the following code that creates a figure with multiple subplots using add_subplot. What is the shape of the axes array after running this code?

Matplotlib

import matplotlib.pyplot as plt
fig = plt.figure()
axes = [fig.add_subplot(2, 2, i) for i in range(1, 5)]
print(len(axes))

A 2

B 4

C 1

D 0

💡 Hint

Each call to add_subplot adds one subplot to the figure.

The code creates 4 subplots arranged in a 2x2 grid. The list 'axes' contains one Axes object per subplot, so its length is 4.

❓ data_output

intermediate

What is the type of the object returned by add_subplot?

After running the code below, what is the type of the variable ax?

Matplotlib

import matplotlib.pyplot as plt
fig = plt.figure()
ax = fig.add_subplot(111)
print(type(ax))

A <class 'matplotlib.axes._subplots.AxesSubplot'>

B <class 'matplotlib.figure.Figure'>

C <class 'list'>

D <class 'tuple'>

💡 Hint

add_subplot returns an Axes object representing a subplot.

The add_subplot method returns an AxesSubplot object which is a type of Axes used for plotting.

❓ visualization

advanced

Identify the subplot layout from the code

Given the code below, what is the layout of the subplots created in the figure?

Matplotlib

import matplotlib.pyplot as plt
fig = plt.figure()
ax1 = fig.add_subplot(2, 3, 1)
ax2 = fig.add_subplot(2, 3, 4)
ax3 = fig.add_subplot(2, 3, 6)
plt.show()

A 3 rows and 2 columns with subplots at positions 2, 4, and 6

B 3 rows and 2 columns with subplots at positions 1, 4, and 6

C 2 rows and 3 columns with subplots at positions 1, 2, and 3

D 2 rows and 3 columns with subplots at positions 1, 4, and 6

💡 Hint

The first two arguments to add_subplot define rows and columns.

The code creates a 2x3 grid of subplots. The third argument specifies the position in row-major order. Positions 1, 4, and 6 correspond to the first subplot in the first row, first subplot in the second row, and last subplot in the second row respectively.

🔧 Debug

advanced

Why does this add_subplot call raise an error?

Examine the code below. Why does the call to add_subplot(3, 2, 7) raise an error?

Matplotlib

import matplotlib.pyplot as plt
fig = plt.figure()
ax = fig.add_subplot(3, 2, 7)

A The position index 7 is invalid for a 3x2 grid (max is 6)

B The number of columns cannot be 2 in add_subplot

C The number of rows cannot be 3 in add_subplot

D add_subplot requires only two arguments, not three

💡 Hint

The third argument must be between 1 and rows*columns inclusive.

For a 3 rows by 2 columns grid, the maximum position index is 6. Using 7 is out of range and causes an error.

🚀 Application

expert

How to create a figure with 3 subplots stacked vertically using add_subplot?

You want to create a figure with 3 subplots stacked vertically (one column, three rows). Which code snippet correctly creates these subplots and stores them in a list axes?

A axes = [fig.add_subplot(3, 3, i) for i in range(1, 4)]

B axes = [fig.add_subplot(1, 3, i) for i in range(1, 4)]

C axes = [fig.add_subplot(3, 1, i) for i in range(1, 4)]

D axes = [fig.add_subplot(1, 1, i) for i in range(1, 4)]

💡 Hint

Rows come first, then columns, then position.

To stack subplots vertically, use 3 rows and 1 column. Positions 1 to 3 create the three subplots stacked vertically.