how to annotate heatmap with text in matplotlib

Question

I am plotting a heatmap in matplotlib using:

plt.pcolor(rand(5,5))

how can I annotate the heatmap with the actual numbers plotted? meaning in each cell of the plotted heatmap, put the value corresponding to that cell in the 5x5 matrix passed to pcolor . thanks.

Answer 1

There is no automatic feature to do such a thing, but you could loop through each point and put text in the appropriate location:

import matplotlib.pyplot as plt
import numpy as np

data = np.random.rand(5, 4)
heatmap = plt.pcolor(data)

for y in range(data.shape[0]):
    for x in range(data.shape[1]):
        plt.text(x + 0.5, y + 0.5, '%.4f' % data[y, x],
                 horizontalalignment='center',
                 verticalalignment='center',
                 )

plt.colorbar(heatmap)

plt.show()

HTH

Answer 2

The seaborn heatmap does the job automatically, by setting annot=True .

See this for an example.