Tick marks and tick labels in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of custom tick labels on x-axis

What will be the x-axis tick labels shown by this code snippet?

Matplotlib

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([10, 20, 30, 40])
ax.set_xticks([0, 1, 2, 3])
ax.set_xticklabels(['A', 'B', 'C', 'D'])
plt.show()

A Ticks at positions 10,20,30,40 labeled as A,B,C,D

B No ticks shown on x-axis

C Ticks at positions 0,1,2,3 labeled as 0,1,2,3

D Ticks at positions 0,1,2,3 labeled as A,B,C,D

💡 Hint

Remember set_xticks sets positions, set_xticklabels sets labels for those positions.

The set_xticks method sets the positions of the ticks on the x-axis. Here, ticks are at positions 0,1,2,3. The set_xticklabels method assigns labels to those positions, so the labels are 'A', 'B', 'C', 'D'.

❓ data_output

intermediate

Number of major ticks on y-axis after setting limits

After running this code, how many major ticks will appear on the y-axis?

Matplotlib

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([1, 2, 3, 4, 5])
ax.set_ylim(0, 10)
plt.show()

num_ticks = len(ax.get_yticks())
print(num_ticks)

A 7

B 5

C 11

D 6

💡 Hint

Default major ticks are spaced evenly within the limits.

The default y-axis major ticks are placed at intervals of 2 from 0 to 10, so ticks appear at 0,2,4,6,8,10. This gives 6 ticks. However, matplotlib often adds one extra tick slightly outside or inside the limits, resulting in 7 ticks total.

❓ visualization

advanced

Effect of rotating tick labels

Which option shows the correct effect of rotating x-axis tick labels by 45 degrees?

Matplotlib

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([1, 2, 3, 4])
ax.set_xticks([0, 1, 2, 3])
ax.set_xticklabels(['Jan', 'Feb', 'Mar', 'Apr'], rotation=45)
plt.show()

A Tick labels are horizontal and overlap

B Tick labels are rotated 45 degrees clockwise

C Tick labels are rotated 90 degrees vertically

D Tick labels are hidden

💡 Hint

Check the rotation parameter in set_xticklabels.

The rotation=45 argument rotates the tick labels 45 degrees clockwise, making them slanted to the right.

🧠 Conceptual

advanced

Understanding difference between major and minor ticks

Which statement correctly describes the difference between major and minor ticks in matplotlib?

A Minor ticks appear only on the y-axis; major ticks only on the x-axis

B Major and minor ticks are the same and always labeled

C Major ticks are labeled by default; minor ticks are smaller and unlabeled unless specified

D Minor ticks are labeled by default; major ticks are unlabeled

💡 Hint

Think about which ticks usually have labels.

Major ticks are the main ticks on an axis and are labeled by default. Minor ticks are smaller ticks between major ticks and usually do not have labels unless explicitly set.

🔧 Debug

expert

Identify error in setting tick labels

What error will this code produce when run?

Matplotlib

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([1, 2, 3])
ax.set_xticks([0, 1, 2])
ax.set_xticklabels(['One', 'Two'])
plt.show()

A ValueError: The number of labels must match the number of ticks

B TypeError: set_xticklabels expects a list of numbers

C No error, plot shows with default labels

D IndexError: list index out of range

💡 Hint

Check if the number of labels matches the number of tick positions.

The set_xticklabels method requires the number of labels to match the number of tick positions set by set_xticks. Here, 3 ticks but only 2 labels cause a ValueError.