Add a vertical label to matplotlib colormap legend

Question

This code enables me to plot a colormap of a "3d" array [X,Y,Z] (they are 3 simple np.array of elements). But I can't succeed in adding a vertical written label at the right of the colorbar legend.

import numpy as np
import matplotlib.pyplot as plt

fig = plt.figure("Color MAP 2D+")

contour = plt.tricontourf(X, Y, Z, 100, cmap="bwr")

plt.xlabel("X")
plt.ylabel("Y")
plt.title("Color MAP 2D+")

#Legend
def fmt(x, pos):
    a, b = '{:.2e}'.format(x).split('e')
    b = int(b)
    return r'${} \times 10^{{{}}}$'.format(a, b)
import matplotlib.ticker as ticker
plt.colorbar(contour, format=ticker.FuncFormatter(fmt))

plt.show()

It's anoying to not get an easy answer from google... can someone help me ?

You forgot to give a problem description. What is the problem with the code you show? What is the result? In how far is it not what you're expecting. See [ask] and [mcve]. — ImportanceOfBeingErnest, Dec 04 '17 at 17:11

score 19 · Accepted Answer · answered Dec 04 '17 at 18:48

You are looking to add a label to the colorbar object. Thankfully, colorbar has a set_label function.

in short:

cbar = plt.colorbar(contour, format=ticker.FuncFormatter(fmt))
cbar.set_label('your label here')

In a minimal script:

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.ticker as ticker

X = np.random.uniform(-2, 2, 200)
Y = np.random.uniform(-2, 2, 200)
Z = X*np.exp(-X**2 - Y**2)

contour = plt.tricontourf(X, Y, Z, 100, cmap="bwr")

def fmt(x, pos):
    a, b = '{:.2e}'.format(x).split('e')
    b = int(b)
    return r'${} \times 10^{{{}}}$'.format(a, b)

cbar = plt.colorbar(contour, format=ticker.FuncFormatter(fmt))
cbar.set_label('your label here')

plt.show()

I have an additional question: how can you change the size of the numbers, on the right of the colorbar ? @tom — Agape Gal'lo, Oct 14 '18 at 21:23
@AgapeGal'lo LMGTFY: https://stackoverflow.com/questions/15305737/python-matplotlib-decrease-size-of-colorbar-labels In short: `cbar.ax.tick_params(labelsize=20)` — tmdavison, Oct 15 '18 at 08:28

score 0 · Answer 2 · answered Dec 04 '17 at 17:09

0

I believe your code is working. See this example:

import numpy as np
import matplotlib.pyplot as plt
from sklearn import datasets

iris = datasets.load_iris().data
X = iris[:,0]
Y = iris[:,1]
Z = iris[:,2]

fig = plt.figure("Color MAP 2D+")

contour = plt.tricontourf(X, Y, Z, 100, cmap="bwr")

plt.xlabel("X")
plt.ylabel("Y")
plt.title("Color MAP 2D+")

#Legend
def fmt(x, pos):
    a, b = '{:.2e}'.format(x).split('e')
    b = int(b)
    return r'${} \times 10^{{{}}}$'.format(a, b)

import matplotlib.ticker as ticker
plt.colorbar(contour, format=ticker.FuncFormatter(fmt))

plt.show()

Output:

answered Dec 04 '17 at 17:09

Scott Boston

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OP code works as well as yours do, but neither yours or theirs adds a legend to the right of the colormap (look at the image the OP has posted in a recent edit). – gboffi Dec 04 '17 at 17:35
Thanks but I want to add a legend on the side. – Agape Gal'lo Dec 04 '17 at 17:38
What do you want the legend to say? The color bar is a legend of the Z values in the graph. – Scott Boston Dec 04 '17 at 17:41
Sorry, the proper word was "label". By the way, do you know how to change the size of the figures in the colorbar ? @ScottBoston – Agape Gal'lo Oct 14 '18 at 21:26

Add a vertical label to matplotlib colormap legend

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