How to Add a Horizontal Line to an Existing Plot in Python?

Plotting a Horizontal Line on an Existing Plot

Adding a horizontal line to an existing plot in Python can be achieved using the axhline (axis horizontal line) function from the matplotlib.pyplot module. This function allows you to draw a line parallel to the x-axis at a specified y-coordinate.

Syntax:

plt.axhline(y=y-coordinate, **kwargs)

Arguments:

• y: The y-coordinate of the horizontal line.

• Additional keyword arguments can be passed to customize the line's appearance, such as:

  • color: The color of the line (default: 'black')
  • linestyle: The style of the line (default: 'solid')

Example:

To plot a horizontal line at y = 0.5:

import matplotlib.pyplot as plt

plt.axhline(y=0.5, color='r', linestyle='-')
plt.show()

This will display a graph with a red dashed line drawn horizontally at y = 0.5.

Note: The axhline function only draws a line parallel to the x-axis. If you wish to draw a vertical line parallel to the y-axis, use the axvline function instead.

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