Custom tick formatters in Matplotlib - Mini Project: Build & Apply

Custom Tick Formatters with Matplotlib

📖 Scenario: You are creating a simple line chart to show daily temperatures over a week. The x-axis shows days as numbers (1 to 7), but you want to display the day names instead (like Mon, Tue, Wed, etc.).

🎯 Goal: Build a matplotlib plot with custom tick labels on the x-axis using a custom tick formatter function.

📋 What You'll Learn

Create a list of temperatures for 7 days.

Create a list of day names for the x-axis labels.

Write a custom tick formatter function to convert day numbers to day names.

Apply the custom tick formatter to the x-axis.

Display the plot with the custom labels.

💡 Why This Matters

🌍 Real World

Custom tick formatters are used in data visualization to make charts clearer and more user-friendly by showing labels that people understand easily.

💼 Career

Data scientists and analysts often customize plots to communicate insights effectively to non-technical audiences.

1

Create temperature data and day numbers

Create a list called temperatures with these exact values: [22, 21, 23, 24, 20, 19, 18]. Also create a list called days with numbers from 1 to 7.

Matplotlib

# Create the list temperatures and the list days
# Your code here

Need a hint?

Use square brackets to create lists. The days list should have numbers 1 through 7.

2

Create day names list

Create a list called day_names with these exact strings: ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"].

Matplotlib

temperatures = [22, 21, 23, 24, 20, 19, 18]
days = [1, 2, 3, 4, 5, 6, 7]
# Create the list day_names
# Your code here

Need a hint?

Use square brackets and quotes to create a list of strings.

3

Write custom tick formatter function

Import matplotlib.pyplot as plt and matplotlib.ticker as mticker. Then write a function called day_formatter that takes a parameter x and returns the day name from day_names at index int(x) - 1. Use mticker.FuncFormatter to create a formatter called formatter using day_formatter.

Matplotlib

import matplotlib.pyplot as plt
import matplotlib.ticker as mticker

# Write the day_formatter function and create formatter
# Your code here

Need a hint?

The formatter function must accept two parameters: x and pos (pos can be optional). Use int(x) - 1 to get the correct index.

4

Plot data and apply custom tick formatter

Create a plot using plt.plot(days, temperatures). Then set the x-axis major formatter to formatter using plt.gca().xaxis.set_major_formatter(formatter). Finally, display the plot with plt.show().

Matplotlib

import matplotlib.pyplot as plt
import matplotlib.ticker as mticker

temperatures = [22, 21, 23, 24, 20, 19, 18]
days = [1, 2, 3, 4, 5, 6, 7]
day_names = ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"]

def day_formatter(x, pos=None):
    return day_names[int(x) - 1]

formatter = mticker.FuncFormatter(day_formatter)

# Plot the data and apply the custom formatter
# Your code here

Need a hint?

Use plt.plot() to draw the line. Use plt.gca().xaxis.set_major_formatter(formatter) to apply the custom labels. Then call plt.show() to display.