[FIXED] Take only part of matrix in Python

Issue

given a matrix A, e.g. A = np.array([[1,2,3,4],[5,6,7,8]]) and two lists one of row indices and one of column indices, e.g. row=(0,1), column=(0,2) I want to extract the corresponding rows and columns of matrix A in python, so in this example I want the result to be np.array([[1, 3], [5,7])). I know how to adress a single entry in a matrix, but not all within a list, moreover I am always loosing the structure. So far the best result I got was with A[row, column], which does not return all indices listed, only A=np.array(([1,7])). I also know that there exists a slicing command, but this only works for consecutive rows and columns which is not the case.

Thank you very much in advance!

Solution

It looks like you want:

A[np.array(row)[:,None], column]

output:

array([[1, 3],
       [5, 7]])

intermediate:

np.array(row)[:,None]

array([[0],
       [1]])

Answered By - mozway