add only specific colums in array - python

Question

I have two numpy arrays, lets say

A = array([ [a11, a12, a13], [a21, a22, a23], [a31, a32, a33] ])
B = array([ [b11, b12, b13], [b21, b22, b23], [b31, b32, b33] ])

and I want to get (EDITED)

C = array([ [a11, a12+b12, a13], [a21, a22+b22, a23], [a31, a32+b32, a33] ])

I could achieve this with for-loop, but I believe there must be a more elegant way in Python.

xnx · Accepted Answer · 2014-12-09 16:35:31Z

2

Can you not simply do the following:

C = A.copy()
C[1] += B[1]    # (or appropriate indexes)

OK -- edited solution:

C = A.copy()
C[:,1] += B[:,1]

answered Dec 9, 2014 at 16:35

xnx

25.7k11 gold badges75 silver badges117 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

sorry I wrote the C array wrong. It's supposed to be C = array([ [a11, a12+b12, a13], [a21, a22+b22, a23], [a31, a32+b32, a33] ])

but I see your answer is correct anyway - I can just use C = A.copy() C[:,1] += B[:,1] works fine