matplotlib: binary heat plot

Question

Let's say I have a 10x10 matrix, that is comprised or just 0s and 1s, represented as a list of lists. How could I use matplotlib to represent such a matrix as a grid of red and black squares? (red for 1, black for 0).

I've search extensively, but the closest I could find was Plot a black-and-white binary map in matplotlib, but the colors are floats less than 1. Once I get 1s in the data, the plot goes awry. Can anyone help? Or point to specific matplotlib documentation that would help me overcome this?

Answer 1

You need what's known as a ListedColorMap:

import numpy as np
import matplotlib.pyplot as plt
import matplotlib as mpl

# random data
x = np.random.random_integers(0, 1, (10, 10))

fig, ax = plt.subplots()

# define the colors
cmap = mpl.colors.ListedColormap(['r', 'k'])

# create a normalize object the describes the limits of
# each color
bounds = [0., 0.5, 1.]
norm = mpl.colors.BoundaryNorm(bounds, cmap.N)

# plot it
ax.imshow(x, interpolation='none', cmap=cmap, norm=norm)