Matplotlib 曲线下区域条件颜色

Question

I'm trying to fill the area between two line plots as such:

import matplotlib.pyplot as plt
import numpy as np


ROCE = np.array([-7.0,-14.0,-11.0,8.0,7.0,17.0,10.0,9.0])
WACC = np.array([4.5, 5.1, 4.7, 3.4, 2.9, 3.7, 3.6, 3.9])
YEAR = np.array([2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019])

fig, ax = plt.subplots(1,1)
ax.plot(YEAR, ROCE, color = 'blue')
ax.plot(YEAR, WACC, color = 'black')
ax.fill_between(YEAR, ROCE, WACC, where=ROCE >= WACC, facecolor='green')
ax.fill_between(YEAR, ROCE, WACC, where=ROCE <= WACC, facecolor='red')

I'm however having an issue at the point where the lines cross as can be seen in the attached image. I suspect I'll have to interpolate the line points. Any idea how one fixes this?

Thanks!

Plot

Answer 1

Default, fill_between only looks at the given values. But it also has an option to interpolate to find the exact crossing points for the where parameter.

import matplotlib.pyplot as plt
import numpy as np

ROCE = np.array([-7.0,-14.0,-11.0,8.0,7.0,17.0,10.0,9.0])
WACC = np.array([4.5, 5.1, 4.7, 3.4, 2.9, 3.7, 3.6, 3.9])
YEAR = np.array([2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019])

fig, ax = plt.subplots(1,1)
ax.plot(YEAR, ROCE, color = 'blue')
ax.plot(YEAR, WACC, color = 'black')
ax.fill_between(YEAR, ROCE, WACC, where=ROCE >= WACC, interpolate=True, facecolor='green')
ax.fill_between(YEAR, ROCE, WACC, where=ROCE <= WACC, interpolate=True, facecolor='red')
plt.show()