python - setting colours in matplotlab pcolor

Question

I want to plot something like the second following image in python using matplotlib:

The code behind this is here:

#!/usr/bin/env python

from pylab import *

Z = rand(6,10)

subplot(2,1,1)
c = pcolor(Z)
title('default: no edges')

subplot(2,1,2)
c = pcolor(Z, edgecolors='k', linewidths=4)
title('thick edges')

show()

Now, I have a list of booleans and I just want to draw a grey rectangle for each True value and a red one for each False value.

Say I just have this:

a = array([True,False],[False,False])

What value in [0,1] should I assign to True and to False?

Answer 1

An easy way to do this is to make a custom colormap. In your case you can make a colormap with just 2 values.

from pylab import *
import matplotlib.colors

figure(figsize=(3,9))
Z = rand(6,10)

subplot(3,1,1)
c = pcolor(Z)
title('default: no edges')

subplot(3,1,2)
c = pcolor(Z, edgecolors='k', linewidths=4)
title('thick edges')
# use Z values greater than 0.5 as an example
Zbool = Z > 0.5

subplot(3,1,3)
cmap = matplotlib.colors.ListedColormap(['red','grey'])
c = pcolor(Zbool, edgecolors='k', linewidths=4, cmap=cmap)
title('thick boolean edges gray')

show()