How to Display Dates on the X-Axis of a Pandas Line Plot?

Pandas Dataframe line plot display date on xaxis

When creating a line plot of a Pandas Dataframe with datetime values on the x-axis, it's important to consider the compatibility between Pandas and matplotlib datetime handling. By default, Pandas and matplotlib use different datetime formats, which can lead to issues with axis formatting.

Problem Background:

Your code snippet illustrates this issue: using pd.to_datetime to convert the 'date' column to datetime objects and setting it as the index creates a Pandas datetime axis. However, adding the DateFormatter directly to this axis doesn't produce the expected date formatting.

Ursache:

The mismatch arises because Pandas uses its own datetime format, which differs from the one used by matplotlib. Attempting to mix these formats can lead to unexpected results.

Solution:

To address this incompatibility, you have two options:

1. Enable x-axis compatibility in Pandas:

Add x_compat=True when plotting the dataframe. This instructs Pandas to use matplotlib's datetime formatting for the x-axis.

df.plot(x_compat=True)

2. Use matplotlib directly for datetime formatting:

Instead of using Pandas' built-in plotting capabilities, you can create a plot using matplotlib directly. This allows you to use matplotlib's full range of datetime formatting options.

plt.plot(df['date'], df['ratio1'])

Using the DateFormatter from matplotlib's dates module, you can achieve the desired date formatting:

ax = df.plot(x_compat=True, figsize=(6, 4))
ax.xaxis.set_major_locator(dates.DayLocator())
ax.xaxis.set_major_formatter(dates.DateFormatter('%d\n\n%a'))
ax.invert_xaxis()
ax.get_figure().autofmt_xdate(rotation=0, ha="center")

By utilizing these methods, you can ensure that the x-axis of your line plot displays dates properly, avoiding any inconsistencies between Pandas and matplotlib datetime handling.

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