Python/Matplotlib – Colorbar Range and Display Values

Question

When using matplotlib with a contour plot, I’m having trouble getting the colorbar to display as I want. I’ve read through numerous similar examples, but have still not been able to get what I want.

In the image below, I want two things changed. I want the minimum value and maximum values to be display on the color bar (the max should be 2.0 and the min -0.1). These two values should be at the very edge of the colorbar. Also, I want the colorbar to display the value at every color transition. For example. in the plot below, between 2.1 and 1.8, there is another color transition where the value isn’t displayed.

I think I may need to use norm, but it hasn’t worked for me so far.

enter image description here

Code:

import numpy as np
import matplotlib.pyplot as plt

xi = np.array([0., 0.5, 1.0])
yi = np.array([0., 0.5, 1.0])
zi = np.array([[0., 1.0, 2.0],
               [0., 1.0, 2.0],
               [-0.1, 1.0, 2.0]])

plt.contour(xi, yi, zi, 15, linewidths=0.5, colors='k')
plt.contourf(xi, yi, zi, 15, cmap=plt.cm.jet)
plt.colorbar()
plt.show()

Asked By: Scott B

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Source

Answer 1

If I understand correctly what you want, I think this should do it:

import numpy as np
import matplotlib.pyplot as plt

xi = np.array([0., 0.5, 1.0])
yi = np.array([0., 0.5, 1.0])
zi = np.array([[0., 1.0, 2.0],
               [0., 1.0, 2.0],
               [-0.1, 1.0, 2.0]])

v = np.linspace(-.1, 2.0, 15, endpoint=True)
plt.contour(xi, yi, zi, v, linewidths=0.5, colors='k')
plt.contourf(xi, yi, zi, v, cmap=plt.cm.jet)
x = plt.colorbar(ticks=v)
print x
plt.show()

enter image description here

Answered By: tom10

Answer 2

Alternative:


    import numpy as np
    import matplotlib.pyplot as plt
    
    xi = np.array([0., 0.5, 1.0])
    yi = np.array([0., 0.5, 1.0])
    zi = np.array([[0., 1.0, 2.0],
                   [0., 1.0, 2.0],
                   [-0.1, 1.0, 2.0]])
    
    v = np.linspace(-.1, 2.0, 15, endpoint=True)
    
    fig, ax = plt.subplots()
    
    plt.contour(xi, yi, zi, v, linewidths=0.5, colors='k')
    ContourPlot = plt.contourf(xi, yi, zi, v, cmap=plt.cm.jet)
    
    ColorBar = fig.colorbar(ContourPlot) # Add a colorbar to a plot
    ColorBar.set_ticks(v)
    plt.show()

Answered By: Dan Doe

Python/Matplotlib – Colorbar Range and Display Values

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