Date formatting with mdates in Matplotlib

Introduction

Date formatting helps show dates clearly on charts. It makes graphs easier to read and understand.

You want to show time series data like stock prices or weather changes.

You need to customize how dates appear on the x-axis of a plot.

You want to display dates in a specific style, like 'Jan 2024' or '2024-01-01'.

You want to improve the look of date labels to avoid overlap or clutter.

Syntax

Matplotlib

import matplotlib.dates as mdates

ax.xaxis.set_major_formatter(mdates.DateFormatter('format_string'))

Replace 'format_string' with the date format you want, like '%Y-%m-%d'.

This code sets how the major ticks on the x-axis show dates.

Examples

Shows dates as year-month-day, e.g., 2024-06-01.

Matplotlib

ax.xaxis.set_major_formatter(mdates.DateFormatter('%Y-%m-%d'))

Shows dates as abbreviated month and day, e.g., Jun 01.

Matplotlib

ax.xaxis.set_major_formatter(mdates.DateFormatter('%b %d'))

Shows only the year, e.g., 2024.

Matplotlib

ax.xaxis.set_major_formatter(mdates.DateFormatter('%Y'))

Sample Program

This code plots values over 5 days in June 2024. It formats the x-axis dates as 'Jun 01, 2024'. The dates are rotated to avoid overlap.

Matplotlib

import matplotlib.pyplot as plt
import matplotlib.dates as mdates
import datetime

# Create some dates
dates = [datetime.date(2024, 6, i) for i in range(1, 6)]
values = [10, 15, 13, 17, 14]

fig, ax = plt.subplots()
ax.plot(dates, values)

# Format the x-axis dates
ax.xaxis.set_major_formatter(mdates.DateFormatter('%b %d, %Y'))

# Rotate date labels for better readability
plt.xticks(rotation=45)

plt.title('Sample Date Formatting with mdates')
plt.tight_layout()
plt.show()

Important Notes

Use plt.xticks(rotation=45) to rotate date labels for clarity.

Common date format codes: %Y = year, %m = month number, %b = abbreviated month, %d = day.

Always import matplotlib.dates as mdates to access date formatters.

Summary

Date formatting makes time data easy to read on plots.

Use mdates.DateFormatter with a format string to set date style.

Rotate labels if they overlap for better visualization.