python. combine two lists in the same lenth

Question

The problem is to build extended lists out of using two same length lists. for example, there is

qq=['a','b','c']
ww=['d','e','f']

my_function(qq,ww)

#I want to see output like:
output = [['a','b','c'],['a','b','f'],['a','e','c'],['a','e','f'],['d','e','f'],['d','e','c'],['d','b','f'],['d','b','c']]

all the combinations of making the same length list with a constraint of:

if a is chosen then d cannot be chosen, same logic,
if b is chosen then e cannot be chosen,
if c is chosen then f cannot be chosen.

The important thing is the elements' position in the list.

so the function takes two same length list of strings. and returns the list of the combinations. How should I write this?

Have you already tried something? [Read here](https://stackoverflow.com/help/how-to-ask) — crissal, May 29 '20 at 20:50

azro · Accepted Answer · 2020-05-29T21:18:36.873

8

You want, from your 2 lists, to do the product of the pairs [a,d] * [b,e] * [c,f]. Using zip to pair, and product to combine them all makes the whole to

take just one element of each pair, so one element per indice, with zip
build all the combinations betwween the pairs, with product

from itertools import product
def custom_product(valuesA, valuesB):
    return list(product(*zip(valuesA, valuesB))) # return list of tuple

def custom_product(valuesA, valuesB):
    return list(map(list, product(*zip(valuesA, valuesB)))) # return list of list

`CODE DEMO`

edited May 29 '20 at 21:18

answered May 29 '20 at 20:55

azro

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But when I tried with valuesA = ['a'] and valuesB = ['b'] it gave me [('a',),('b',)] with the comma on the touple. – minjunkim7767 May 29 '20 at 21:14
@minjunkim7767 this is just to know that it is a tuple, do you want to get list instead of tuple ? like `[[a], [b]]` , – azro May 29 '20 at 21:16
@minjunkim7767 I've add it in my post – azro May 29 '20 at 21:18
Thanks alot! Appreciate it! – minjunkim7767 May 29 '20 at 21:20
Hi @azro I have another question here. Do you think you can take a look at it? https://stackoverflow.com/questions/62097511/python-sequencially-select-parts-of-a-string-similar-to-ngram – minjunkim7767 May 30 '20 at 03:47

Jacob Brazeal · Answer 2 · 2020-05-29T21:01:14.920

Here's a recursive solution.

The base case is of course when each list has just one item and we take each list as possible output. For longer lists, you find all the possible arrangements of the lists not counting the first items, and then return those items with each of the first items.


def solve(list1, list2):
     if len(list1) != len(list2):
         throw ValueError("Lists should be same length")
     if len(list1) == 0:
         return []
     if len(list1) == 1:
         return [[list1[0], list2[0]]
     children = solve(list1[1:], list2[1:])
     return [[list1[0]] + child for child in children] + [[list2[0]] + child for child in children]]

python. combine two lists in the same lenth

2 Answers2

CODE DEMO

`CODE DEMO`