How do I Add Horizontal Lines to Existing Plots in Matplotlib?

Plotting Horizontal Lines on Existing Figures with axhline

Adding horizontal lines to existing plots is a simple task using Matplotlib. The axhline function creates a horizontal axis line at a specified y-coordinate.

Syntax:

matplotlib.pyplot.axhline(y=y_value, color=color, linestyle=linestyle)

Parameters:

• y: The y-coordinate of the horizontal line.
• color: The color of the line.
• linestyle: The linestyle of the line (e.g., '-', '--', ':').

Example:

To plot a horizontal line at y = 0.5, you can use the following code:

import matplotlib.pyplot as plt

# Create a figure and axes
fig, ax = plt.subplots()

# Add a horizontal line
ax.axhline(y=0.5, color='r', linestyle='-')

# Show the figure
plt.show()

This will produce the following figure:

[Image of a plot with a horizontal line at y = 0.5]

Customizing the Horizontal Line:

You can customize the appearance of the horizontal line by setting the color and linestyle parameters. For example, the following code would plot a dashed blue line at y = 0.7:

import matplotlib.pyplot as plt

# Create a figure and axes
fig, ax = plt.subplots()

# Add a horizontal line
ax.axhline(y=0.7, color='blue', linestyle='--')

# Show the figure
plt.show()

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