Slicing of a NumPy 2d array, or how do I extract an mxm submatrix from an nxn array (n>m)?

Question

I want to slice a NumPy nxn array. I want to extract an arbitrary selection of m rows and columns of that array (i.e. without any pattern in the numbers of rows/col

Answer 1

I have a similar question here: Writting in sub-ndarray of a ndarray in the most pythonian way. Python 2 .

Following the solution of previous post for your case the solution looks like:

columns_to_keep = [1,3] 
rows_to_keep = [1,3]

An using ix_:

x[np.ix_(rows_to_keep, columns_to_keep)] 

Which is:

array([[ 5,  7],
       [13, 15]])