Make a contour plot by using three 1D arrays

Question

As the title indicates I would like to make a contour plot by using three 1D arrays. Let's say that

x = np.array([1,2,3])

and

y = np.array([1,2,3])

and

z = np.array([20,21,45])

To do a contourplot in matplotlib i meshed the x and y coordinate as X,Y = meshgrid(x,y) but then the z array must also be a 2D array. How do I then turn z into a 2d array so it can be used?

Answer 1

Your z is wrong. It needs to give the values at every point of the mesh. If z is a function of x and y, calculate z at what I refer to as X_grid below:

import numpy as np
import matplotlib.pyplot as plt

def f(x):
    return (x[:,0]**2 + x[:,1]**2)

x = np.array([1,2,3])
y = np.array([1,2,3])
xx, yy = np.meshgrid(x, y)
X_grid = np.c_[ np.ravel(xx), np.ravel(yy) ]
z = f(X_grid)

z = z.reshape(xx.shape)

plt.contour(xx, yy, z)