How to combine every element of a list to the other list

Question

Suppose there are two lists:

['a', 'b', 'c'], ['d', 'e', 'f']

what I want is:

'ad','ae','af','bd','be','bf','cd','ce','cf'


 first_list = ['a', 'b', 'c']
second_list = ['d', 'e', 'f']
combined_list = []
for i in first_list:
    for j in second_list:
        combined_list.append(i + j)
print(combined_list)

my question is if there are not only two lists, how to improve the code? for example,

first_list = ['a', 'b', 'c']
second_list = ['d', 'e', 'f']
third_list = ['g','h','q']
print ['adg','adh','adq','aeg','aeh',.......]

guys,are there any generalizable ways to show n lists..I mean what if there are more than three lists?

Alexander · Answer 1 · 2017-03-07T04:14:35.480

2

This is called a cartesian product.

import itertools

first_list = ['a', 'b', 'c']
second_list = ['d', 'e', 'f']
third_list = ['g','h','q']
lists = [first_list, second_list, third_list]

cartesian_product = [''.join(x) for x in itertools.product(*lists)]

print(cartesian_product)

Output:

['adg', 'adh', 'adq', 'aeg', 'aeh', 'aeq', 'afg', 'afh', 'afq',
 'bdg', 'bdh', 'bdq', 'beg', 'beh', 'beq', 'bfg', 'bfh', 'bfq',
 'cdg', 'cdh', 'cdq', 'ceg', 'ceh', 'ceq', 'cfg', 'cfh', 'cfq']

You can try it online, here.

Here's an example implementation of a cartesian production function, which you can try out here.

def cartesian_product(*lists):
    if not lists: # base case
        return [[]]
    else:
        this_list = lists[0]
        remaining_lists = lists[1:]
        return [
          [x] + p
            for x in this_list
              for p in cartesian_product(*remaining_lists)
        ]

edited Mar 07 '17 at 04:14

answered Mar 07 '17 at 03:57

Alexander

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thank you ! btw, do you know any way in loop, I mean, using for...instead of itertools – Linda dadad Mar 07 '17 at 04:02
Sure, I can cook up the implementation. Give me some time. – Alexander Mar 07 '17 at 04:05
@Lindadadad I would use a generator expression to simplify this, but you could convert it to for loops if you wish – Alexander Mar 07 '17 at 04:15

score 0 · Answer 2 · answered Mar 07 '17 at 03:57

0

I haven't tested this but this should work.

first_list = ['a', 'b', 'c']
second_list = ['d', 'e', 'f']
third_list = ['g','h','q']
combined_list = []
for i in first_list:
    for j in second_list:
        for k in third_list:
            combined_list.append(i + j + k)
print(combined_list)

answered Mar 07 '17 at 03:57

user82395214

829
14
37

1

This isn't generalizable to any arbitrary number of lists. The down vote isn't mine, btw – Alexander Mar 07 '17 at 03:57
yes，it's not generalizable...if there are n lists? – Linda dadad Mar 07 '17 at 03:59

How to combine every element of a list to the other list

2 Answers2