add legend to colorbar 1

add legend to colorbar

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

#discrete color scheme
cMap = ListedColormap(['white', 'green', 'blue','red'])

data = np.random.rand(4, 4)
fig, ax = plt.subplots()
heatmap = ax.pcolor(data, cmap=cMap)

cbar = plt.colorbar(heatmap)['0','1','2','>3'])
cbar.set_label('# of contacts', rotation=270)

# put the major ticks at the middle of each cell
ax.set_xticks(np.arange(data.shape[1]) + 0.5, minor=False)
ax.set_yticks(np.arange(data.shape[0]) + 0.5, minor=False)

column_labels = list('ABCD')
row_labels = list('WXYZ')
ax.set_xticklabels(column_labels, minor=False)
ax.set_yticklabels(row_labels, minor=False)

Here is what the above code is Doing:
1. Create a discrete color scheme
2. Create some random data
3. Create a figure and a subplot
4. Create a heatmap from the data
5. Create a colorbar
6. Set the ticks and labels
7. Invert the y-axis
8. Show the plot

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