Matplotlib: Colorbar ticks and color independent of values in parent plot

Question

Let us suppose I have two 2D arrays given below I want to plot contourf plots for. I will plot the two contourf using two subplots.

import numpy as np
import matplotlib.pyplot as plt
a = np.array([
    [1, 2, 2],
    [0, 1, 2],
    [0, 0, 1],
])

b = np.array([
    [4, 5, 5],
    [3, 4, 5],
    [3, 3, 4],
])

Specifications:

• I want to have one colorbar in each my subplots [Solved].
• I want both my colorbars to have ticks from 0 to 5 [Not Solved].
• I want the want colors within the contours and colorbars to reflect the true range from 0 to 5 [Solved].

Currently, I have the following code which solves two out of the three requirements.

z1lim = [0, 5]
levels = 5
ticks = np.linspace(*z1lim, levels)
fig, ax = plt.subplots(ncols=2, figsize=(16, 6)) 

# contourf 0
cntf0 = ax[0].contourf(
    a,
    cmap='viridis', 
    levels=levels, 
    vmin=z1lim[0],
    vmax=z1lim[1],
)
# colorbar 0
cbar0 = fig.colorbar(
    cntf0,
    ticks=ticks,
    ax=ax[0]
)


# contourf 1
cntf1 = ax[1].contourf(
    b,
    cmap='viridis', 
    levels=levels, 
    vmin=z1lim[0],
    vmax=z1lim[1],
)
# colorbar 1
cbar1 = fig.colorbar(
    cntf1,
    ticks=ticks,
    ax=ax[1]
)

Current Plots

Looking at the current results, I am not able to have the colorbars that have the range from 0 to 5. It would be great if someone can give me a working code that would result in colorbars having the ticks from 0 to 5.

Answer 1

You take 5 levels in each plot, but do not specify where they lie. Hence the one plot cannot know about the other. Make sure to use the same levels in both cases:

import numpy as np
import matplotlib.pyplot as plt
a = np.array([ [1, 2, 2], [0, 1, 2], [0, 0, 1], ])
b = np.array([ [4, 5, 5], [3, 4, 5], [3, 3, 4], ])

z1lim = [0, 5]
levels = ticks = np.linspace(*z1lim, 11)

fig, ax = plt.subplots(ncols=2, figsize=(16, 6)) 

# contourf 0
cntf0 = ax[0].contourf( a, cmap='viridis',  levels=levels)
# colorbar 0
cbar0 = fig.colorbar( cntf0, ticks=ticks, ax=ax[0] )

# contourf 1
cntf1 = ax[1].contourf( b, cmap='viridis',  levels=levels)
# colorbar 1
cbar1 = fig.colorbar( cntf1, ticks=ticks, ax=ax[1] )

plt.show()