How to Format the Datetime Axis of a Matplotlib Graph to Display Year and Month Only?

Changing the Datetime Axis Format on a Matplotlib Graph

When plotting a time series with a datetime index, it is often desirable to format the x-axis labels to display a specific level of detail, such as year-month combinations. This can be achieved by using the DateFormatter class from the matplotlib.dates module.

Problem:

A user wants to plot a series indexed by datetime, but the graph displays time values down to the second, resulting in cluttered labels. The desired format is to show only year and month (e.g., "2014-01" or "2016 March").

Solution:

To achieve the desired formatting, follow these steps:

1. Import the necessary modules: numpy (np), pandas (pd), matplotlib.pyplot (plt), and matplotlib.dates (mdates).
2. Create a sample DataFrame with a datetime index and random values.
3. Create a figure and axes using plt.subplots().
4. Plot the series by calling ax.plot(df.index, df.values).
5. Specify the x-axis ticks using ax.set_xticks(df.index).
6. Use DateFormatter to specify the major and minor tick formatters. In this example, mdates.DateFormatter("%Y-%m") is used to display dates in the format "YYYY-MM".
7. Rotate the x-axis tick labels (optional) using _ = plt.xticks(rotation=90) .

The resulting graph will display the series data with the desired datetime axis formatting, showing only the year and month values.

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