matplotlib twinx inside a loop

Question

I have a loop which for a certain condition (occurs e.g 3 times), I'd like to plot two dataset with twinx, so e.g at the end I have 3 plots on left-y and 3 plots on right-y. When I use the usual twinx, the loop takes incorrect values for right-y. How should I modify this example code to get them correct? Thank you very much!

import numpy as np
import matplotlib.pyplot as plt

x=np.linspace(0,10,100)
A=5

fig,ax=plt.subplots()

for i in range(0,10):
  A=i**2
  if(i%3==0):
    ax.plot(x,A*np.sin(x),'-ro')
    ax2=ax.twinx()
    ax2.plot(x,A*x,'-bp')
plt.show()

Here is the output.

tnknepp · Accepted Answer · 2016-05-25 20:00:58Z

2

You need to move your "ax2" definition outside the loop (see below). However, this makes seven plots, four on left, three on right. You need to update your "if" condition.

[![import numpy as np
import matplotlib.pyplot as plt

x=np.linspace(0,10,100)
A=5

fig,ax=plt.subplots()
ax2=ax.twinx()

for i in range(0,10):
  A=i**2
  if(i%3==0):
    ax.plot(x,A*np.sin(x),'-ro')
    ax2.plot(x,A*x,'-bp')
plt.show()][1]][1]

answered May 25, 2016 at 20:00

tnknepp

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2 Comments

Joonho Park Over a year ago

I am exactly in the same situation and I want to add legend. Can you add legend for each plot and display legend?

tnknepp Over a year ago

@JoonhoPark I think what you want is covered in this answer: stackoverflow.com/a/5487005/1678467

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