Table of Contents
To draw a horizontal line in matplotlib, you can use the Axes.axhline() function. This function takes in the y-axis value where the line needs to be drawn, and any other optional parameters such as color, linewidth, linestyle, etc. You can also use the plot() function to draw a horizontal line. When using the plot() function, you specify the x and y coordinates of the points on the line, with all of the y-coordinates being the same. Both methods can be used to successfully draw a horizontal line in matplotlib.
You can use the following syntax to draw a horizontal line in Matplotlib:
import matplotlib.pyplot as plt #draw vertical line at y=10 plt.axhline(y=10)
The following examples show how to use this syntax in practice with the following pandas DataFrame:
import pandas as pd
#create DataFrame
df = pd.DataFrame({'x': [1, 2, 3, 4, 5, 6, 7, 8],
'y': [5, 7, 8, 15, 26, 39, 45, 40]})
#view DataFrame
df
x y
0 1 5
1 2 7
2 3 8
3 4 15
4 5 26
5 6 39
6 7 45
7 8 40
Example 1: Draw One Horizontal Line
The following code shows how to draw one horizontal line on a Matplotlib plot:
import matplotlib.pyplot as plt
#create line plot
plt.plot(df.x, df.y)
#add horizontal line at y=10
plt.axhline(y=10, color='red', linestyle='--')
Example 2: Draw Multiple Horizontal Lines
The following code shows how to draw multiple horizontal lines on a Matplotlib plot:
import matplotlib.pyplot as plt
#create line plot
plt.plot(df.x, df.y)
#add horizontal line at y=10
plt.axhline(y=10, color='red', linestyle='--')
#add horizontal line at y=30
plt.axhline(y=30, color='black', linestyle='-')
Example 3: Draw Multiple Horizontal Lines with Legend
The following code shows how to draw multiple horizontal lines on a Matplotlib plot and add a legend to make the lines easier to interpret:
import matplotlib.pyplot as plt
#create line plot
plt.plot(df.x, df.y)
#add horizontal line at y=10
plt.axhline(y=10, color='red', linestyle='--', label='First Line')
#add horizontal line at y=30
plt.axhline(y=30, color='black', linestyle='-', label='Second Line')
#add legend
plt.legend()
Note: Refer to the for a complete list of colors and linestyles you can apply to horizontal lines.