Sum each elements in several lists in Python

Question

I have this code:

list_1 = [11, 22]
list_2 = [33, 44, 55 ,66]
list_3 = [77, 88 ,99]

I want to sum each elements in lists. i.e. 11 + 33 + 77, 11 + 33 + 88, … 22 + 33 + 77, 22 + 33 + 88… and put all the sums into a final list

I have these lines:

list_1 = [11, 22]
list_2 = [33, 44, 55 ,66]
list_3 = [77, 88 ,99]

result = []

for L_1 in list_1:
    for L_2 in list_2:
        for L_3 in list_3:
            result.append(L_1 + L_2 + L_3)

print result                   # to output all elements
print list(set(result))     # to not showing duplicates

The codes work well but looked clumsy. If there are 20 or more lists to take part in the calculation, it doesn’t looked good at all.

Could you please show me a better way?

@Transhuman, thank you for your help. your lines are good for learning. could you please resume your answer? — Mark K, Dec 29 '17 at 06:44
@cᴏʟᴅsᴘᴇᴇᴅ - Thanks, I mis-understood the question. — Transhuman, Dec 29 '17 at 06:44
Also see https://stackoverflow.com/questions/533905/get-the-cartesian-product-of-a-series-of-lists — PM 2Ring, Dec 29 '17 at 06:49

PM 2Ring · Accepted Answer · 2017-12-29T06:47:49.813

3

This sort of combination is called the Cartesian product. You can get it using itertools.product.

from itertools import product

list_1 = [11, 22]
list_2 = [33, 44, 55, 66]
list_3 = [77, 88, 99]

result = {sum(t) for t in product(list_1, list_2, list_3)}
print(sorted(result))

output

[121, 132, 143, 154, 165, 176, 187]

You can even use product if you don't know in advance how many lists you have:

all_lists = list_1, list_2, list_3
result = {sum(t) for t in product(*all_lists)}

The product iterator yields tuples of the items from the iterables that you pass it. We then pass those tuples to the built-in sum function to perform the addition.

Here's what the "raw" output from product looks like:

from itertools import product

list_1 = [1, 2]
list_2 = [3, 4]
list_3 = [5, 6]

all_lists = list_1, list_2, list_3
for t in product(*all_lists):
    print(t)

output

(1, 3, 5)
(1, 3, 6)
(1, 4, 5)
(1, 4, 6)
(2, 3, 5)
(2, 3, 6)
(2, 4, 5)
(2, 4, 6)

edited Dec 29 '17 at 06:47

answered Dec 29 '17 at 06:38

PM 2Ring

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This gives the product, but doesn't the asker want to sum the values instead? – Deem Dec 29 '17 at 06:40
@Windmill Which it also does – cs95 Dec 29 '17 at 06:41
Does it? Sorry, was just going off the number of values given in the output. – Deem Dec 29 '17 at 06:42
@PM 2Ring, thank you for the teaching! – Mark K Dec 29 '17 at 06:44
1

@Windmill The number of items in `result` is small because we've collected them in a set to eliminate duplicates. – PM 2Ring Dec 29 '17 at 06:48

score 1 · Answer 2 · answered Dec 29 '17 at 06:43

1

map(sum, product(*lists))

Demo:

>>> from itertools import product
>>> lists = [11, 22], [33, 44, 55, 66], [77, 88, 99]
>>> map(sum, product(*lists))
[121, 132, 143, 132, 143, 154, 143, 154, 165, 154, 165, 176, 132, 143, 154, 143, 154, 165, 154, 165, 176, 165, 176, 187]

answered Dec 29 '17 at 06:43

Stefan Pochmann

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`set(map(sum, product(*lists)))` based on Op's requirements. – cs95 Dec 29 '17 at 06:45
You mean their *"put all the sums into a final list"*? – Stefan Pochmann Dec 29 '17 at 06:46
@StefanPochmann, very good! thank you for teaching. :) – Mark K Dec 29 '17 at 06:47
No, I mean by the `list(set(result))` in the list line. – cs95 Dec 29 '17 at 06:48
@cᴏʟᴅsᴘᴇᴇᴅ That's not in the stated "requirements". Also, it's commented with "to not *showing* duplicates" (emphasis my interpretation). And it's literally not their `result`. – Stefan Pochmann Dec 29 '17 at 06:50
Nice use of `map`, and I guess it's not too advanced for the OP. – PM 2Ring Dec 29 '17 at 07:00

Sum each elements in several lists in Python

2 Answers2