Pyplot - change color of line if data is less than zero?

Question

I am trying to figure out if there is anything built into pyplot that will change the color of my line depending on whether or not the data is negative or positive. For exam

Answer 1

If you use a scatter plot you can give each point a different color:

x = range(1)
x = range(10)
y = [i - 5 for i in x]
c = [i < 0 for i in y]
plt.scatter(x, y, c=c, s=80)

Answer 2

You can conditionally plot data in your axes object, using a where like syntax (if you're used to something like Pandas).

ax.plot(x[f(x)>=0], f(x)[f(x)>=0], 'g')
ax.plot(x[f(x)<0],  f(x)[f(x)<0],  'r')

Technically, it's splitting and plotting your data in two sets, but it's fairly compact and nice.

Answer 3

I would just make two datasets and setting the right masks. By using that approach i wont have lines between different positive parts.

import matplotlib.pyplot as plt
import numpy as np

signal = 1.2*np.sin(np.linspace(0, 30, 2000))
pos_signal = signal.copy()
neg_signal = signal.copy()

pos_signal[pos_signal <= 0] = np.nan
neg_signal[neg_signal > 0] = np.nan

#plotting
plt.style.use('fivethirtyeight')
plt.plot(pos_signal, color='r')
plt.plot(neg_signal, color='b')
plt.savefig('pos_neg.png', dpi=200)
plt.show()