How to create a heat map in python that ranges from green to red?

Question

I\'m trying to plot log ratios from the range -3 to 3 and want negative ratios to be green and positive to be red, with a log ratio of 0 (center) to be white in color. None

Answer 1

How about the following that uses LinearSegmentedColormap:

import matplotlib.pyplot as plt
import numpy as np
from matplotlib.colors import LinearSegmentedColormap


cmapGR = LinearSegmentedColormap(
    'GreenRed',
    {
        'red':  ((0.0, 0.0, 0.0),
                (0.5, 1.0, 1.0),
                (1.0, 1.0, 1.0)),
        'green':((0.0, 1.0, 1.0),
                (0.5, 1.0, 1.0),
                ( 1.0, 0.0, 0.0)),
        'blue': ((0.0, 0.0, 0.0),
                (0.5, 1.0, 1.0),
                (1.0, 0.0, 0.0))
    },)

plt.imshow(np.array([np.arange(200) for i in range(200)]), cmap=cmapGR)
plt.show()

It produces the following

See e.g. http://matplotlib.org/examples/pylab_examples/custom_cmap.html for more uses and other examples.