Highlight matplotlib points that go over or under a threshold in colors based on the amount the boundaries are crossed

Question

I have a graph that looks like this:

And the code I\'m running to get this graph (one of a sequence of

Answer 1

You can use boolean masks to select points that fulfill certain conditions, and plot them:

import matplotlib.pyplot as plt
import numpy as np

std = 0.1
N = 100

x = np.linspace(0, 1, N)
expected_y = np.sin(2 * np.pi * x)
y = expected_y + np.random.normal(0, std, N)

dist = np.abs(y - expected_y) / std

mask1 = (1 < dist) & (dist <= 2)
mask2 = dist > 2

plt.fill_between(x, expected_y - 0.1, expected_y + 0.1, alpha=0.1)
plt.fill_between(x, expected_y - 0.2, expected_y + 0.2, alpha=0.1)

plt.plot(x, y)
plt.plot(x[mask1], y[mask1], 'x')
plt.plot(x[mask2], y[mask2], 'x')


plt.tight_layout()
plt.savefig('mp_points.png', dpi=300)

Result:

Answer 2

Use boolean indexing to identify these points and plot them separately:

import numpy as np
x = np.random.rand(20)

b = x > 0.7

print(b)
print(x[b])