Matplotlib Second Y-Axis Label Example

This article will show you how to add the second y-axis with a label on Matplotlib plots.

1. How To Add The Second Y-Axis Label On Matplotlib Plot.

  1. First plot the first curve with the default x, y-axis.
    # plot the first curve.
    plt.plot(x,y1)
  2. Then call the matplotlib.pyplot module’s twinx() method to add the second y-axis on the figure right side.
    # add another y-axis.
    plt.twinx()
  3. Now you can plot the second curve, and the second curve will use the same x-axis and the second y-axis.
    # plot the second curve, the curve line has green color.
    plt.plot(x,y2,'g')

2. Add The Second Y-Axis On Matplotlib Plot Example.

  1. Below is the example full source code.
    import numpy as np
    import matplotlib.pyplot as plt
    
    def second_y_axis_example():
        
        # create a numpy array contains integer number 1 - 10..
        x=np.arange(1,10)
        print('x: ', x)
        
        # calculate y1.
        y1 = x + x
        print('y1: ', y1)
        
        # calculate y2.
        y2 = np.log(x)
        print('y2: ', y2)
    
        # plot the first curve.
        plt.plot(x,y1)
        
        # set the matplotlib plot title.
        plt.title('matplotlib add second y-axis example')
    
        # add another y-axis.
        plt.twinx()
        
        # plot the second curve, the curve line has green color.
        plt.plot(x,y2,'g')
        
        # display the plot.
        plt.show()
           
    
    if __name__ == '__main__':
        
        second_y_axis_example()
  2. When you run the above example, you can get the below figure.
    matplotlib-add-second-y-axis-example

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