How to Correctly Plot Dates on the X-Axis in Matplotlib?

Understanding Date Plotting in matplotlib

Plotting information against dates can be a common task when working with time-series data. However, converting and plotting dates can occasionally lead to errors.

The Issue: Converting and Plotting Dates

In the example provided, the user encountered a "ValueError: year is out of range" error while attempting to plot dates on the x-axis. The issue arose from the conversion process, specifically when using num2date.

The Solution: Utilizing the plot Function

To resolve this issue, consider using the plot function instead of plot_date. This method takes a list of dates and automatically recognizes them as dates, allowing you to bypass the conversion step.

Step 1: Convert Dates to datetime.date Objects

Convert the date strings to instances of datetime.date for easier handling. For example:

<code class="python">import datetime as dt

dates = ['01/02/1991', '01/03/1991', '01/04/1991']
x = [dt.datetime.strptime(d, '%m/%d/%Y').date() for d in dates]</code>

Step 2: Configure X-Axis for Date Formatting

Set up the x-axis to display dates correctly using DateFormatter and DayLocator from matplotlib.dates:

<code class="python">import matplotlib.pyplot as plt
import matplotlib.dates as mdates

plt.gca().xaxis.set_major_formatter(mdates.DateFormatter('%m/%d/%Y'))
plt.gca().xaxis.set_major_locator(mdates.DayLocator())</code>

Step 3: Generate the Plot

Finally, plot the data using the set-up x-axis and the y-axis data:

<code class="python">plt.plot(x, y)
plt.gcf().autofmt_xdate()</code>

This method eliminates the conversion errors and correctly plots the dates on the x-axis, providing a clear representation of time-based data.

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