set colorbar range with contourf

Question

This would appear to be a duplicate of this question:

Set Colorbar Range in matplotlib

Essentially I want to set the colorbar range to set limits, e.g. 0 to 2. When I use vmin and vmax, the range of colors in contourf is correctly set, but colorbar only shows the clipped range, i.e. the solution in the link doesn't seem to work when using contourf. Am I missing something obvious?

import numpy as np
import matplotlib.pyplot as plt
fld=np.random.rand(10,10)
img=plt.contourf(fld,20,cmap='coolwarm',vmin=0,vmax=2)
plt.colorbar(img)

Resulting in

How can I force the colorbar range to be 0 to 2 with contourf?

Answer 1

contourf indeed works a bit differently than other ScalarMappables. If you specify the number of levels (20 in this case) it will take them between the minimum and maximum data (approximately). If you want to have n levels between two specific values vmin and vmax you would need to supply those to the contouring function

levels = np.linspace(vmin, vmax, n+1)
plt.contourf(fld,levels=levels,cmap='coolwarm')

Complete code:

import numpy as np
import matplotlib.pyplot as plt
fld=np.random.rand(10,10)
levels = np.linspace(0,2,21)
img=plt.contourf(fld,levels=levels,cmap='coolwarm')
plt.colorbar(img)
plt.show()