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I have 5 lists that contain some data:

a = [52, 265, 1, 98, 26]
b = [42, 85, 45, 2, 3, 8, 632]
c = [7, 731, 92, 65, 28, 62]
d = [3, 5, 44, 55]
e = [15, 35, 850, 6, 18, 41]

What I want to do is get the sum of the values of every possible combination, for example:

a[0] + b[0] + c[0] + d[0] + e[0] = **121**
...
a[4] + b[6] + c[5] + d[3] + e[5] = **816**

This needs to be done is the fastest way possible, because in my code the length of these lists is bigger, thus making the calculation of all possibilities extremely time demanding.

My first idea was using nested for loops, but that's not fast enough. I imagine some transformations and some magic could be done with NumPy to speed up this process.

  • Python is the wrong language if you want this to be done in the fastest possible way. – timgeb Dec 27 '17 at 18:29
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    I strongly suspect that you'll need to avoid actually computing all these sums to solve your underlying problem efficiently. – user2357112 Dec 27 '17 at 18:30
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    this is a trick question. .. you should not be fully exploring the search space – Joran Beasley Dec 27 '17 at 18:32
  • The core idea of the analysis I'm making is to go through all of the possibilities in order to find the very best one, so this is probably the only way of doing that. –  Dec 27 '17 at 18:35
  • well since you have not defined "best" this is definately a true statement from where we are sitting ... – Joran Beasley Dec 27 '17 at 18:37
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    This is almost certainly an [XY Problem](https://meta.stackexchange.com/a/66378/344593). What do you need all the sums for? What is the end goal? – TemporalWolf Dec 27 '17 at 18:49

2 Answers2

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the fastest way to actually sum all the combinations(you actually want the product, not the combinations) is to generate them and sum them 

print([(x,sum(x)) for x in itertools.product(my_list1,my_list2,my_list3,...)])

but I suspect that the secret is to not check all the products, but instead to intelligently select specific values to narrow your search space

Joran Beasley
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  • Based on my tests this seems to be the fastest way of doing it, and it's also very simple. The only thing I changed was `(x,sum(x))` to `sum(x)`. Thanks, Joran. –  Dec 29 '17 at 00:05
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You want something like this ?

a = [52, 265, 1, 98, 26]
b = [42, 85, 45, 2, 3, 8, 632]
c = [7, 731, 92, 65, 28, 62]
d = [3, 5, 44, 55]
e = [15, 35, 850, 6, 18, 41]

import itertools

print(list(map(lambda x:sum(x),itertools.product(a,b,c,d,e))))

output:

119, 139, 954, 110, 122, 145, 121, 141, 956, 112, 124, 147, 160, 180, 995, 151, 163, 186, 171, 191, 1006, 162, 174, 197, 843, 863, 1678, 834, 846, 869, 845, 865, 1680, 836, 848, 871, 884, 904, 1719, 875, 887, 910, 895, 915, 1730, 886, 898, 921, 204, 224, 1039, 195, 207, 230, 206, 226, 1041, 197, 209, 232, 245, 265, 1080, 236, 248, 271, 256, 276, 1091, 247, 259, 282, 177, 197, 1012, 168, 180, 203, 179, 199, 1014, 170, 182, 205, 218, 238, 1053, 209, 221, 244, 229, ....
Aaditya Ura
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