How to make Matplotlib scatterplots transparent as a group?

Question

I\'m making some scatterplots using Matplotlib (python 3.4.0, matplotlib 1.4.3, running on Linux Mint 17). It\'s easy enough to set alpha transparency for each point individuall

Answer 1

Interesting question, I think any use of transparency will result in the stacking effect you want to avoid. You could manually set a transparency type colour to get closer to the results you want,

import matplotlib.pyplot as plt
import numpy as np

def points(n=100):
    x = np.random.uniform(size=n)
    y = np.random.uniform(size=n)
    return x, y
x1, y1 = points()
x2, y2 = points()
fig = plt.figure(figsize=(4,4))
ax = fig.add_subplot(111, title="Test scatter")
alpha = 0.5
ax.scatter(x1, y1, s=100, lw = 0, color=[1., alpha, alpha])
ax.scatter(x2, y2, s=100, lw = 0, color=[alpha, alpha, 1.])
plt.show()

The overlap between the different colours are not included in this way but you get,