List comprehension: Creating new list by adding multiple values in single list

Question

Given a list containing monthly numerical data, how can I easily convert this into quarterly data?

x= [5,8,3,4,5,6,1,2,5,3,11,8] #monthly data for Jan-Dec

Desired output:

[5+8+3, 4+5+6, 1+2+5, 3+11+8] #converted to quarterly data

I wanted to do something like [a+b+c for a,b,c in x] but x it says x is not iterable.

I don't think this is a duplicate. I am specifically looking for a list comprehension solution.

Possible duplicate of [How do you split a list into evenly sized chunks?](https://stackoverflow.com/questions/312443/how-do-you-split-a-list-into-evenly-sized-chunks) — Mureinik, Sep 15 '18 at 15:56

sacuL · Accepted Answer · 2018-09-15T16:02:08.360

1

A list comprehension way:

[sum([x[i],x[i+1],x[i+2]]) for i in range(0,len(x),3)]
#[16, 15, 8, 22]

Or in a nicer way (thanks @JonClements):

[sum(x[i:i+3]) for i in range(0, len(x), 3)]

And a numpy way:

import numpy as np

np.sum(np.array(x).reshape(-1,3),axis=1)
#array([16, 15,  8, 22])

edited Sep 15 '18 at 16:02

answered Sep 15 '18 at 15:58

sacuL

4

That `sum` part can be simplified... `[sum(x[i:i+3]) for i in range(0, len(x), 3)]` – Jon Clements Sep 15 '18 at 16:00
Dude @JonClements is a beast, he's everywhere on here, ha I even watched the youtube clip of his Dr. Who quote, this did is a monster <3 – vash_the_stampede Sep 15 '18 at 17:09

score 0 · Answer 2 · answered Sep 15 '18 at 17:13

Not getting to crazy you could just slice them up and then work with each group

x= [5,8,3,4,5,6,1,2,5,3,11,8]

a, b, c, d = x[:3], x[3:6], x[6:9], x[9:12]

print(a, b, c, d)

(xenial)vash@localhost:~/python/stack_overflow$ python3.7 slice_q.py 
[5, 8, 3] [4, 5, 6] [1, 2, 5] [3, 11, 8]

From here if you want to sum each group you could do something like this

lista = [a, b, c, d,]

for i in lista:
    print(sum(i))

2 Answers2