Merging list based on values

April 17, 2022

I have 4 lists of different lengths, simplifying:

main_lst1= ["a", "b", "c", "d", "e", "f", "g"] - with all values

lst1 = ["a", "c", "d", "e", "f"]
lst2 = ["a", "b", "c", "d", "e", "g"]
lst3 = ["c", "d", "e", "f", "g"]

and I need to combine/ merge that lists to get:

lst1 = ["a", 0, "c", "d", "e", "f", 0]
lst2 = ["a", "b", "c", "d", "e", 0, "g"]
lst3 = [0, 0, "c", "d", "e", "f", "g"]

I hope that is enough explanation what I need to get.
Kindly help.

>Solution :

I’m going to assume that lst1, lst2, and lst3 are alphabetically sorted and that they would only have the characters from main_lst1.

Something like this should work:

main_lst1 = ["a", "b", "c", "d", "e", "f", "g"]

lst1 = ["a", "c", "d", "e", "f"]
lst2 = ["a", "b", "c", "d", "e", "g"]
lst3 = ["c", "d", "e", "f", "g"]

for cur_lst in (lst1, lst2, lst3):
    cur_i = 0
    while len(cur_lst) != len(main_lst1):
        if cur_lst[cur_i] != main_lst1[cur_i]:
            cur_lst.insert(cur_i, 0)
        cur_i += 1
        if cur_i == len(cur_lst):
            cur_lst.append(0)
            break

    print(cur_lst)

Basically, I loop over the list and insert 0 when I find that the character doesn’t match that of the main list. Of course, if the assumptions I made earlier aren’t correct, then this solution will need more alterations to work.

Edit: Also note that since lists are mutable in python, the above code would alter the original lists.