How do I extract a submatrix to run a for loop and calculate a specific parameter?

Question

I am new to python and I am asking for your help :)

I have written a general function to calculate a parameter on an matrix. The script works, but it is on the whole matrix.

I need the script to work in a for loop for each individual subject, which unfortunately consists of many rows.

The loop should work regardless of the actual subject number, so that if someone is not in the dataset the function knows how to go ahead and return the actual subject number to me.

Here an example

Thank you :)