CODEWITHSUNDEEP
pythonmatplotlibheatmap
mikael
mikael

Reputation: 2317

matplotlib 3D heatmap

How to use pcolormesh to plot a heatmap? I have three lists of equal size, X, Y and Z. When I do 

plt.pcolormesh(X, Y, Z)

I get "ValueError: need more than 1 value to unpack" and when I do 

plt.pcolormesh(np.array(zip(X, Y)), Z)

I get this: enter image description here

Upvotes: 0

Views: 4655

Answers (1)

Molly
Molly

Reputation: 13610

You have to look at the documentation for pcolor to see the requirements for the input arguments to pcolormesh. x, y and c can't be lists of numbers, they have be lists of lists or two dimensional numpy arrays. You need two dimensional arrays because pcolor and pcolormesh draw a quadrilateral for each value of c with corners defined in x and y. The x and y values that correspond to a particular value in c are determined by their location in the array.

From the documentation:

"X and Y, if given, specify the (x, y) coordinates of the colored quadrilaterals; the quadrilateral for C[i,j] has corners at:

(X[i, j], Y[i, j]), (X[i, j+1], Y[i, j+1]), (X[i+1, j], Y[i+1, j]), (X[i+1, j+1], Y[i+1, j+1])."

To change your x and y lists into two dimensional numpy arrays you can use meshgrid. 

import matplotlib.pyplot as plt
import numpy as np

x = np.arange(0,11)
y = np.arange(0,11)
xv, yv = np.meshgrid(x,y)
c = np.random.rand(10,10)

plt.pcolormesh(xv,yv,c)

plt.show()

pcolormesh example

Upvotes: 1

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