How to extract non-consecutive rows and columns of a matrix?

Question

How do I extract from a matrix rows and columns that are not consecutive. For example, in this matrix how do i extract rows 1,2 and 4 with columns 1, 2 and 4?

import numpy as np

a = np.matrix([[1, 2, 3, 4, 5],
               [6, 7, 8, 9, 10],
               [11, 12, 13, 14, 15],
               [16, 17, 18, 19, 20],
               [18, 19, 20, 21, 22]])

So the new matrix should be:

b = ([[7, 8 , 10],
     [12, 13, 15],
     [19, 20, 22]])

Answer 1

In the doc section linked by hpaulj, see example starting with From a 4x3 array the corner elements should be selected using advanced indexing.

Specifically, the paragraph that starts This broadcasting can also be achieved using the function ix_:

In your case, rows are [1, 2, 4] and same for columns, so

rows = np.array([1, 2, 4], dtype=np.intp)
columns = np.array([1, 2, 4], dtype=np.intp)
b = a[np.ix_(rows, columns)]