CODEWITHSUNDEEP
pythonnumpy
Medulla Oblongata
Medulla Oblongata

Reputation: 3961

Python subtract first element from each respective row of matrix

I want to subtract the first value of a row from the rest of the elements of that row, so for

import numpy as np

z = np.array([[1,2,3,4],[4,5,6,7],[7,8,9,9]])

for n in range(0,3):
    znew = z[n,:]-z[n,0]

znew should be np.array([[0,1,2,3],[0,1,2,3],[0,1,2,2]]). How can I do this? It kind of seems trivial.

Upvotes: 2

Views: 1515

Answers (1)

Ashwini Chaudhary
Ashwini Chaudhary

Reputation: 251011

You can do this by taking advantage of broadcasting:

>>> z - z[:,0][:, None] # or z - z[:,0][:, np.newaxis]
array([[0, 1, 2, 3],
       [0, 1, 2, 3],
       [0, 1, 2, 2]])

Upvotes: 3

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