Convert X,Y,Z Values to Matrixplot

Question

I have the following lists:

x_list = [7,10,3,9,9]
y_list = [2,5,1,3,2]

z_list = [4,1,5,2,3]

For each x value and y value there is a zvalue. For example: x=7and y=2have the zvalue of 4.

I would like to convert this into a matrix such as:

… to be able to create a matrix-plot with the correct x- and y- axis and a colorbar (colorbar is missing here, and it would be nice to have the zero values as black color):

It is rather straightforward to do in Excel, but I am having difficulties doing it in python, since I am quite new to matplotlib.

Edit

I might use plt.imshow() to make the plot

Answer 1

NumPy's unique and meshgrid functions are your friends here to set up the proper grid from your coordinates. Then, you just need to find the proper indices in the resulting X and Y, that correspond to your coordinates. Finally, in some all-zero Z matrix with the same dimensions as X and Y, you can set the elements at the just found indices to your original z data.

Here's some code:

import numpy as np

x = np.array([7, 10, 3, 9, 9])
y = np.array([2,  5, 1, 3, 2])
z = np.array([4,  1, 5, 2, 3])

# Calculate X, Y grid from x and y, initialize Z data with zero
X, Y = np.meshgrid(np.unique(x), np.unique(y))
Z = np.zeros(X.shape)

# Find proper indices in grid, and set Z values accordingly
idx = np.squeeze([np.argwhere(np.logical_and(X == x[idx], Y == y[idx])) for idx in np.int32(np.arange(x.size))])
Z[idx[:, 0], idx[:, 1]] = z
print(Z)

And, the output is:

[[5. 0. 0. 0.]
 [0. 4. 3. 0.]
 [0. 0. 2. 0.]
 [0. 0. 0. 1.]]

Regarding the plotting: I can't think of a Matplotlib function to create a plot similar to the shown. So, maybe give an additional hint, which function you have in mind.

Hope that helps!