Adding y=x to a matplotlib scatter plot if I haven't kept track of all the data points that went in

Question

Here\'s some code that does scatter plot of a number of different series using matplotlib and then adds the line y=x:

import numpy as np, matplotlib.pyplot a         


        

Answer 1

If you set scalex and scaley to False, it saves a bit of bookkeeping. This is what I have been using lately to overlay y=x:

xpoints = ypoints = plt.xlim()
plt.plot(xpoints, ypoints, linestyle='--', color='k', lw=3, scalex=False, scaley=False)

or if you've got an axis:

xpoints = ypoints = ax.get_xlim()
ax.plot(xpoints, ypoints, linestyle='--', color='k', lw=3, scalex=False, scaley=False)

Of course, this won't give you a square aspect ratio. If you care about that, go with Paul H's solution.