Major and minor ticks in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Identify the number of major ticks on the x-axis

Given the following matplotlib code, how many major ticks will appear on the x-axis?

Matplotlib

import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax.plot([0, 1, 2, 3, 4], [10, 20, 25, 30, 40])
ax.xaxis.set_major_locator(plt.MultipleLocator(1))
plt.show()

A 3

B 5

C 4

D 6

💡 Hint

Count the ticks starting from 0 to 4 with step 1.

The major locator is set to place ticks every 1 unit on the x-axis from 0 to 4, so ticks appear at 0,1,2,3,4 totaling 5 ticks.

❓ data_output

intermediate

Output of minor tick positions on y-axis

What are the positions of the minor ticks on the y-axis after running this code?

Matplotlib

import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax.plot([0, 1, 2], [10, 20, 30])
ax.yaxis.set_minor_locator(plt.MultipleLocator(5))
minor_ticks = ax.yaxis.get_minorticklocs()
print(minor_ticks)

A [5. 10. 15. 20. 25. 30.]

B [0. 5. 10. 15. 20. 25. 30.]

C [10. 15. 20. 25. 30.]

D [12.5 17.5 22.5 27.5]

💡 Hint

Minor ticks start at 10 and go up to 30 in steps of 5.

Minor ticks are placed every 5 units on y-axis. The y limits range approximately from 10 to 30, so minor ticks appear at 10,15,20,25,30.

❓ visualization

advanced

Visualize major and minor ticks on both axes

Which option shows the correct plot with major ticks every 2 units and minor ticks every 0.5 units on both axes?

Matplotlib

import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax.plot([0, 1, 2, 3, 4], [0, 1, 4, 9, 16])
ax.xaxis.set_major_locator(plt.MultipleLocator(2))
ax.xaxis.set_minor_locator(plt.MultipleLocator(0.5))
ax.yaxis.set_major_locator(plt.MultipleLocator(5))
ax.yaxis.set_minor_locator(plt.MultipleLocator(1))
plt.show()

A Plot with x-axis major ticks at 0,2,4 and minor ticks every 0.5; y-axis major ticks at 0,5,10,15 and minor ticks every 1

B Plot with x-axis major ticks at 0,1,2,3,4 and minor ticks every 0.2; y-axis major ticks at 0,4,8,12 and minor ticks every 0.5

C Plot with x-axis major ticks at 1,3 and minor ticks every 1; y-axis major ticks at 0,10,20 and minor ticks every 2

D Plot with x-axis major ticks at 0,2,4 and no minor ticks; y-axis major ticks at 0,5,10,15 and minor ticks every 0.5

💡 Hint

Check the locator settings for both axes carefully.

The code sets x major ticks every 2 units (0,2,4) and minor ticks every 0.5 units; y major ticks every 5 units (0,5,10,15) and minor ticks every 1 unit.

🔧 Debug

advanced

Identify the error in minor tick setting

What error will this code raise when setting minor ticks?

Matplotlib

import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax.plot([0, 1, 2], [10, 20, 30])
ax.xaxis.set_minor_locator(plt.MultipleLocator(0))
plt.show()

A ValueError: interval must be > 0

B TypeError: 'MultipleLocator' object is not callable

C No error, plot shows with default minor ticks

D AttributeError: 'AxesSubplot' object has no attribute 'set_minor_locator'

💡 Hint

Check the argument passed to MultipleLocator.

MultipleLocator requires a positive interval. Zero interval causes ValueError.

🚀 Application

expert

Customize ticks to highlight weekends on a time series plot

You have daily data for 14 days starting from Monday. You want to set major ticks on Mondays and minor ticks on other days. Which code snippet correctly sets this using matplotlib's FixedLocator?

Matplotlib

import matplotlib.pyplot as plt
import matplotlib.dates as mdates
import pandas as pd
import numpy as np

dates = pd.date_range('2023-01-02', periods=14)  # Monday start
values = np.random.rand(14)
fig, ax = plt.subplots()
ax.plot(dates, values)

# Your code here to set major ticks on Mondays and minor ticks on other days

plt.show()

A

mondays = mdates.date2num(dates[dates.weekday == 0])
ax.xaxis.set_major_locator(mdates.FixedLocator(mondays))
ax.xaxis.set_minor_locator(mdates.FixedLocator(mondays))

B

mondays = mdates.date2num(dates[dates.weekday == 1])
all_days = mdates.date2num(dates)
ax.xaxis.set_major_locator(mdates.FixedLocator(mondays))
ax.xaxis.set_minor_locator(mdates.FixedLocator(all_days))

C

mondays = mdates.date2num(dates[dates.weekday == 0])
ax.xaxis.set_major_locator(mdates.DayLocator(interval=7))
ax.xaxis.set_minor_locator(mdates.DayLocator(interval=1))

D

mondays = mdates.date2num(dates[dates.weekday == 0])
all_days = mdates.date2num(dates)
ax.xaxis.set_major_locator(mdates.FixedLocator(mondays))
ax.xaxis.set_minor_locator(mdates.FixedLocator(np.setdiff1d(all_days, mondays)))

💡 Hint

Use FixedLocator with dates converted to numbers and exclude Mondays from minor ticks.

Option D correctly sets major ticks on Mondays and minor ticks on all other days by using FixedLocator with date numbers and numpy setdiff1d to exclude Mondays from minor ticks.