fill_between with matplotlib and a where condition of two lists

Question

I am trying to shade the area before the point of intersection of the two curves produced by this example code:

import numpy as np
import matplotlib.pyplot as pl         


        

Answer 1

You are completely right, you need to interpolate. And that is ludicrously complicated, as you need to add the interpolate=True keyword argument to the call to fill_between.

ax.fill_between(x,y1,y2,where=z1>=z2,color='grey', interpolate=True)

Complete code to reproduce:

import numpy as np
import matplotlib.pyplot as plt 

x = np.arange(0,100,10)
y1 = [0,2,4,6,8,5,4,3,2,1]
y2 = [0,1,3,5,6,8,9,12,13,14]

fig = plt.figure()
ax = fig.add_subplot(111)
ax.plot(x,y1,linestyle='-')
ax.plot(x,y2,linestyle='--')

z1 = np.array(y1)
z2 = np.array(y2)

ax.fill_between(x,y1,y2,where=z1>=z2,color='grey',alpha=0.5, interpolate=True)

plt.show()