2d array minus 1d array

Question

In python numpy:

A = [[1,2,3],[4,5,6],[7,8,9]]
b = [2,3,5]

want [1,2,3] -2, [4,5,6]-3, [7,8,9] -5

e.g. ideal result:

[[-1,0,1],[1,2,3],[2,3,4]]

any way solve this without loop?

Mohamed Yilmaz · Accepted Answer · 2019-07-17 14:34:20Z

3

You have not used Numpy at all. It is pretty easy with that. You need to add an extra dimension to b with None or numpy.newaxis and then subtract.

import numpy
A = numpy.array([[1,2,3],[4,5,6],[7,8,9]])
b = numpy.array([2,3,5])

c= A-b[:,None]

print(c)

Output:

[[-1  0  1]
 [ 1  2  3]
 [ 2  3  4]]

answered Jul 17, 2019 at 14:34

Mohamed Yilmaz

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1 Comment

this doesn't use loops unlike the other answers

Zachary Oldham · Accepted Answer · 2019-07-17 14:29:18Z

0

for i in range(0, len(A)):
    cur_arr = A[i]
    for j in range(0, len(cur_arr)):
        cur_arr[j] = cur_arr[j] - B[j]

answered Jul 17, 2019 at 14:29

Zachary Oldham

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Jmonsky · Accepted Answer · 2019-07-17 14:29:29Z

0

Using pure python you are going to need a for loop somewhere.

A_L = [[1,2,3],[4,5,6],[7,8,9]]
B_L = [2,3,5]

sub = lambda a, b : [[x - B for x in A] for A, B in zip(a,b)]

c = sub(A_L,B_L)
print(c)

Outputs: [[-1, 0, 1], [1, 2, 3], [2, 3, 4]]

answered Jul 17, 2019 at 14:29

Jmonsky

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