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.

Practice

1. What do tick marks on a matplotlib graph represent?

easy

A. The color of the graph lines

B. Positions on the axis where values are shown

C. The title of the graph

D. The size of the graph figure

Solution

1. Step 1: Understand the role of tick marks

   Tick marks are small marks along the axis that show where specific values lie.

2. Step 2: Identify what tick marks indicate on a graph

   They help us see the scale and exact positions of data points on the axis.

3. Final Answer:

   Positions on the axis where values are shown -> Option B

4. Quick Check:

   Tick marks = axis positions [OK]

Hint: Tick marks show value positions on axes [OK]

Common Mistakes:

• Confusing tick marks with graph title
• Thinking tick marks control graph color
• Mixing tick marks with figure size

2. Which of the following is the correct way to set custom tick labels on the x-axis in matplotlib?

easy

A. plt.ticklabels([1, 2, 3], ['A', 'B', 'C'])

B. plt.set_xticks(['A', 'B', 'C'])

C. plt.xticks([1, 2, 3], ['A', 'B', 'C'])

D. plt.xlabels([1, 2, 3], ['A', 'B', 'C'])

Solution

1. Step 1: Recall the matplotlib function for setting ticks and labels

   The function plt.xticks() sets both tick positions and their labels on the x-axis.

2. Step 2: Check the syntax of plt.xticks()

   It takes two arguments: a list of positions and a list of labels, like plt.xticks([1, 2, 3], ['A', 'B', 'C']).

3. Final Answer:

   plt.xticks([1, 2, 3], ['A', 'B', 'C']) -> Option C

4. Quick Check:

   Custom x-axis labels use plt.xticks() [OK]

Hint: Use plt.xticks(positions, labels) to set x-axis labels [OK]

Common Mistakes:

• Using non-existent functions like plt.ticklabels
• Confusing tick positions with labels
• Using plt.set_xticks() without labels

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

import matplotlib.pyplot as plt
plt.plot([10, 20, 30])
plt.xticks([0, 1, 2], ['Low', 'Medium', 'High'])
plt.show()

medium

A. A scatter plot with labels 'Low', 'Medium', 'High'

B. A line plot with default numeric x-axis labels 0, 1, 2

C. An error because plt.xticks() is used incorrectly

D. A line plot with x-axis labels 'Low', 'Medium', 'High' at positions 0, 1, 2

Solution

1. Step 1: Understand the plot and xticks usage

   The plot shows points at y-values 10, 20, 30 with default x positions 0, 1, 2.

2. Step 2: Analyze plt.xticks() effect

   plt.xticks([0, 1, 2], ['Low', 'Medium', 'High']) replaces x-axis tick labels at positions 0,1,2 with the given strings.

3. Final Answer:

   A line plot with x-axis labels 'Low', 'Medium', 'High' at positions 0, 1, 2 -> Option D

4. Quick Check:

   xticks sets custom labels at given positions [OK]

Hint: xticks changes labels, not plot type [OK]

Common Mistakes:

• Thinking xticks changes plot type
• Expecting numeric labels after setting strings
• Confusing positions and labels order

4. Identify the error in this code that tries to rotate x-axis tick labels:

import matplotlib.pyplot as plt
plt.plot([1, 2, 3])
plt.xticks(rotation=45)
plt.show()

medium

A. No error; code runs correctly

B. plt.xticks() needs positions and labels to rotate

C. plt.xticks() must be called before plt.plot()

D. rotation argument is not valid in plt.xticks()

Solution

1. Step 1: Check plt.xticks() usage with rotation

   plt.xticks() can be called with rotation parameter alone to rotate existing tick labels.

2. Step 2: Confirm code correctness

   The code plots points and rotates x-axis labels by 45 degrees without needing to specify positions or labels.

3. Final Answer:

   No error; code runs correctly -> Option A

4. Quick Check:

   Rotation works with plt.xticks(rotation=angle) [OK]

Hint: Rotation works without specifying labels [OK]

Common Mistakes:

• Thinking positions are required to rotate labels
• Believing rotation is invalid argument
• Assuming plot order affects xticks rotation

5. You have a bar chart with 5 bars. You want to set custom labels ['A', 'B', 'C', 'D', 'E'] on the x-axis and rotate them 60 degrees for better readability. Which code snippet correctly does this?

hard

A. plt.xticks(range(5), ['A', 'B', 'C', 'D', 'E'], rotation=60)

B. plt.xticks(['A', 'B', 'C', 'D', 'E'], range(5), rotation=60)

C. plt.xticks(rotation=60)
plt.xticks(range(5), ['A', 'B', 'C', 'D', 'E'])

D. plt.xticks(range(5), ['A', 'B', 'C', 'D', 'E'])
plt.xticks(rotation=60)

Solution

1. Step 1: Understand plt.xticks() parameters

   plt.xticks() takes positions as first argument, labels as second, and rotation as a keyword argument.

2. Step 2: Check which option sets labels and rotation together

   plt.xticks(range(5), ['A', 'B', 'C', 'D', 'E'], rotation=60) correctly passes positions, labels, and rotation in one call.

3. Step 3: Analyze other options

   plt.xticks(['A', 'B', 'C', 'D', 'E'], range(5), rotation=60) swaps positions and labels incorrectly; A and C call plt.xticks() twice, which may override settings.

4. Final Answer:

   plt.xticks(range(5), ['A', 'B', 'C', 'D', 'E'], rotation=60) -> Option A

5. Quick Check:

   Set labels and rotation in one plt.xticks() call [OK]

Hint: Use plt.xticks(positions, labels, rotation=angle) [OK]

Common Mistakes:

• Swapping positions and labels arguments
• Calling plt.xticks() twice causing override
• Forgetting to pass rotation argument