如何为散点指定颜色

Question

I'm trying to assign a color to points in a matplotlib scatter plot based on a value that is not related to the x or y value. Each point can be, for example, one of 3 values, so I want three different colors for the 3 possible values. So, there are 3 arrays: x_arr, y_arr and val_arr where each element of val_arr can be 1, 2 or 3. Seems like most of the examples I've seen have the color based on the position in the array, and not based on an independent value.

In order to get a high contrast between the 3 kinds of points for better visibility where there are many points, I've done something like this:

 pt_color = plt.cm.Dark2(np.linspace(0, 1, 3))

What I cannot figure out is how to assign the right color for each value element. Conceptually, I would like to do something like this,

gr.scatter(x_arr, y_arr, c=val_arr, cmap=pt_color)

where each element of val_arr is mapped to a color using pt_color, but the above does not work (I get a TypeError because pt_color is unhashable type).

Any pointers are appreciated.

Answer 1

import matplotlib.pyplot as plt
from numpy.random import random, randint

X = random(10)
Y = random(10)
val_arr = randint(low=0, high=3, size=10)
plt.scatter(X, Y, c=val_arr,
            s=40)
plt.colorbar()
plt.show()

spaces the val_arr values out over the default colormap, and the colorbar explains what the val_arr colors mean.