How to plot a rectangle on a datetime axis using Matplotlib?

To plot a rectangle on a datetime axis using Matplotlib, we need to convert datetime objects to numeric values that Matplotlib can handle. This involves using matplotlib.dates module to work with time-based coordinates.

Required Steps

• Set up the figure and subplot
• Define datetime anchor points for the rectangle
• Convert datetime objects to numeric format using mdates.date2num()
• Create a Rectangle patch with datetime coordinates
• Add the rectangle to the axes using add_patch() method
• Configure datetime formatting for the x-axis
• Set appropriate axis limits and display the plot

Example

Here's how to create a rectangle on a datetime axis ?

from datetime import datetime, timedelta
from matplotlib.patches import Rectangle
import matplotlib.pyplot as plt
import matplotlib.dates as mdates

# Set figure size and layout
plt.rcParams["figure.figsize"] = [7.50, 3.50]
plt.rcParams["figure.autolayout"] = True

# Create figure and subplot
fig = plt.figure()
ax = fig.add_subplot(111)

# Define datetime range for rectangle
startTime = datetime.now()
endTime = startTime + timedelta(seconds=1)

# Convert datetime to numeric format
start = mdates.date2num(startTime)
end = mdates.date2num(endTime)

# Calculate width and create rectangle
width = end - start
rect = Rectangle((start, 0), width, 1, color='red')
ax.add_patch(rect)

# Configure datetime formatting
locator = mdates.AutoDateLocator(minticks=3)
formatter = mdates.AutoDateFormatter(locator)
ax.xaxis.set_major_locator(locator)
ax.xaxis.set_major_formatter(formatter)

# Set axis limits
plt.xlim([start - width, end + width])
plt.ylim([-0.5, 1.5])

plt.show()

Output

The code produces a plot with a red rectangle positioned on a datetime x-axis ?

Key Components

mdates.date2num() ? Converts datetime objects to numeric values that Matplotlib can plot

Rectangle patch ? Creates a rectangular shape with specified position, width, height, and color

AutoDateLocator/Formatter ? Automatically formats datetime labels on the x-axis for better readability

Conclusion

Use mdates.date2num() to convert datetime objects for Matplotlib compatibility. The Rectangle patch combined with proper datetime formatting creates clear time-based visualizations.