How to sum second list from list of list in Python

Question

I would like to sum from list of list as below

array([[[1, 1, 1],
      [2, 2, 2],
      [3, 3, 3],
      [4, 4, 4],
      [5, 5, 5]],

     [[1, 1, 1],
      [2, 2, 2],
      [3, 3, 3],
      [4, 4, 4],
      [5, 5, 5]],

     [[1, 1, 1],
     [2, 2, 2],
     [3, 3, 3],
     [4, 4, 4],
     [5, 5, 5]]]

What i want is to sum like below

   [1,1,1]+[1,1,1]+[1,1,1]  = 9
   [2,2,2]+[2,2,2]+[2,2,2]  = 18
       ....                 = 27
                            = 36
                            = 45

And return a list like below as the final list:

[9,18,27,36,45]

MSS · Accepted Answer · 2023-01-20 08:08:44Z

5

You can use np.sum

a = np.array([[[1, 1, 1],
  [2, 2, 2],
  [3, 3, 3],
  [4, 4, 4],
  [5, 5, 5]],

 [[1, 1, 1],
  [2, 2, 2],
  [3, 3, 3],
  [4, 4, 4],
  [5, 5, 5]],

 [[1, 1, 1],
 [2, 2, 2],
 [3, 3, 3],
 [4, 4, 4],
 [5, 5, 5]]])

res = np.sum(a, axis=(0,2))
# Does reduction along axis 0 and 2 by doing summation.
# numpy takes tuple of axis indices to do reduction 
# simultaneously along those axis.
print(res.tolist())
>> [ 9, 18, 27, 36, 45]

edited Jan 20, 2023 at 8:08

answered Jan 20, 2023 at 6:18

MSS

3,6932 gold badges28 silver badges57 bronze badges

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

2 Comments

foy Over a year ago

thanks , can you explain more on axis (0,2) please

MSS Over a year ago

@foy Summation will be done along axis 0 and 2.

Light · Accepted Answer · 2023-01-20 06:22:00Z

1

import numpy as np
lis=np.array([[[1, 1, 1],
      [2, 2, 2],
      [3, 3, 3],
      [4, 4, 4],
      [5, 5, 5]],

     [[1, 1, 1],
      [2, 2, 2],
      [3, 3, 3],
      [4, 4, 4],
      [5, 5, 5]],

     [[1, 1, 1],
     [2, 2, 2],
     [3, 3, 3],
     [4, 4, 4],
     [5, 5, 5]]])
print(lis.sum(axis=0).sum(axis=1))
easiest I think with numpy.
output

[ 9 18 27 36 45]

answered Jan 20, 2023 at 6:22

Light

1771 silver badge6 bronze badges

Comments

Yash Mehta · Accepted Answer · 2023-01-20 06:20:51Z

0

Using zip()

Code:

import numpy as np
lis=np.array([[[1, 1, 1],
      [2, 2, 2],
      [3, 3, 3],
      [4, 4, 4],
      [5, 5, 5]],

     [[1, 1, 1],
      [2, 2, 2],
      [3, 3, 3],
      [4, 4, 4],
      [5, 5, 5]],

     [[1, 1, 1],
     [2, 2, 2],
     [3, 3, 3],
     [4, 4, 4],
     [5, 5, 5]]])
res=[]

for i in zip(*lis):
    res.append(sum(sum(i)))
print(res)

Output:

[9, 18, 27, 36, 45]

List comprehension:

print([sum(sum(i)) for i in zip(*lis)]) #Same output.

edited Jan 20, 2023 at 6:20

answered Jan 20, 2023 at 6:12

Yash Mehta

2,0024 gold badges13 silver badges21 bronze badges

Comments

Grateful_programmer · Accepted Answer · 2023-01-20 06:22:41Z

-1

a = [[[1, 1, 1],
      [2, 2, 2],
      [3, 3, 3],
      [4, 4, 4],
      [5, 5, 5]],

     [[1, 1, 1],
      [2, 2, 2],
      [3, 3, 3],
      [4, 4, 4],
      [5, 5, 5]],

     [[1, 1, 1],
     [2, 2, 2],
     [3, 3, 3],
     [4, 4, 4],
     [5, 5, 5]]]

result = [sum(x)+sum(y)+sum(z) for x,y,z in zip(a[0], a[1], a[1])]

answered Jan 20, 2023 at 6:22

Grateful_programmer

591 silver badge6 bronze badges

2 Comments

Thomas Wagenaar Over a year ago

Welcome to stackoverflow and thank you for answering your first question. Make sure to add a description of what your code does and how it answers the question!

Community Over a year ago

Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center.

Collectives™ on Stack Overflow

How to sum second list from list of list in Python

4 Answers 4

2 Comments

Comments

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

2 Comments

Comments

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related