Arithmetic Operations on Numpy Array

Question

I have two numpy arrays pcar and out_list.

[[  5.80084178e-05   1.20779787e-02  -2.65970238e-02]
 [ -1.36810406e-02   6.85722519e-02  -2.60280724e-01]
 [  4.21996519e-01  -1.43644036e-01   2.12904690e-01]
 [  3.03098198e-02   1.50170659e-02  -1.09683402e-01]
 [ -1.50776089e-03   7.22369575e-03  -3.71181228e-02]
 [ -3.04448275e-01  -3.66987035e-01   1.44618682e-01]
 [ -1.46744916e-01   3.47112167e-01   3.09550267e-01]
 [  1.16567762e-03   1.72858807e-02  -9.39297514e-02]
 [  1.25896836e-04   1.61310167e-02  -6.00253128e-02]
 [  1.65062798e-02   1.96933143e-02  -4.26540031e-02]
 [ -3.78020965e-03   7.51770012e-03  -3.67852984e-02]]

and

[[-0.01368104  0.06857225 -0.26028072]
 [ 0.42199652 -0.14364404  0.21290469]]

I want to subtraction of out_list from pcar and want to get two different arrays with the results.

Example:

First Array as-

[[ 5   8    5]
 [ 1   2    4]
 [ 7   6    1]]

and Second Array as-

[[ 1   6   2]
 [ 4   5   3]]

then result should be

[[ 4   2   3]
 [ 0   -4   2]
 [ 6    0  -1]]

and

[[ 1   3   2]
 [-3  -3   1]
 [ 3   1  -2]]

I don't get how to subtract between 11 x 3 and 2 x 3 matrices? Do you mean two result that 11 x 3 - 1 x 3 and 11 x 3 - 1 x 3? — emesday
– emesday, Commented Apr 5, 2014 at 15:16
@mskimm Yup I want the results of 11 x 3 - 1 x 3 and 11 x 3 - 1 x 3. — DummyGuy
– DummyGuy, Commented Apr 5, 2014 at 15:19
It is ambiguous what you mean by subtraction here. From a mathematical point of view it is impossible to subtract a 2x3 matrix form a 11x3 one. — j-i-l
– j-i-l, Commented Apr 5, 2014 at 15:20
@jojo I want that 1st row of 2 x 3 array should be deleted from all the rows of 11 x 3 array and so on. So that I will get two atrix of size 11 x 3 — DummyGuy
– DummyGuy, Commented Apr 5, 2014 at 15:23

j-i-l · Accepted Answer · 2014-04-05 15:46:46Z

1

This should do the job:

import numpy as np
a = np.array([[1,2,3],[10,20,30],[100,200,300]])
b = np.array([[1,2,3],[10,20,30]])
result_list = [np.subtract(a,b_x) for b_x in b]
#now you can use the result_list:
print result_list[0]
#>>> [[  0   0   0]
#     [  9  18  27]
#     [ 99 198 297]]

print result_list[1]
#>>>[[ -9 -18 -27]
#    [  0   0   0]
#    [ 90 180 270]]

edited Apr 5, 2014 at 15:46

answered Apr 5, 2014 at 15:28

j-i-l

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3 Comments

DummyGuy Over a year ago

Can I access these two arrays differently so I can do more operations on it?

j-i-l Over a year ago

I'm not completely sure if I understand what you'd like to do, but will edit my answer, just a sec...

j-i-l Over a year ago

consider accepting the answer if it works for you :)

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