以所有可能的排列替换列表中的项目

Question

Let's say I have a list or an array of the type:

mylist = [1, 2, 3, 4]

And I want to replace an item in this list. Normally I would use something like the following:

mylist[2] = 7

That works well. However, can someone explain how to create all possible permutations of mylist when replacing one or more items in mylist . For example, I want to create the following:

[7, 2, 3, 4]
[7, 7, 3, 4]
[7, 2, 7, 4]
[7, 7, 7, 4]
[7, 2, 3, 7]
...(and so on)

I know I can use itertools to generate all possible permutations, but how can I specify that I want to substitute an item in all possible locations in the list before generating the permutations? Here is how I tried to use itertools :

list(itertools.permutations([1,2,3,4,7], 4))

This doesn't work because it doesn't substitute 7 more than one time per permutation, and it also generates permutations that do not include the number 7 .

Answer 1

Use itertools.combinations to find the indices to replace:

replace = 7
mylist = [1, 2, 3, 4]
for i in range(1, len(mylist) + 1):
    for selected in itertools.combinations(range(len(mylist)), i):
        res = mylist[:]
        for n in selected:
            res[n] = replace
        print(res)

Output:

[7, 2, 3, 4]
[1, 7, 3, 4]
[1, 2, 7, 4]
[1, 2, 3, 7]
[7, 7, 3, 4]
[7, 2, 7, 4]
[7, 2, 3, 7]
[1, 7, 7, 4]
[1, 7, 3, 7]
[1, 2, 7, 7]
[7, 7, 7, 4]
[7, 7, 3, 7]
[7, 2, 7, 7]
[1, 7, 7, 7]
[7, 7, 7, 7]

Answer 2

You can create a function and just pass the list and value to that function and you get what you want :

import itertools
def replaced_it(list_1,value):

    final_list = []
    len_=len(list_1)
    track_index = [k for k, j in enumerate(list_1)]
    for i in range(len(track_index) + 1):


        empty_list = [value]
        replaced_one = list_1[:]
        for ia in itertools.permutations(track_index, r=i):
            if ia:
                for i, j in zip(ia, empty_list * len(ia)):
                    replaced_one[i] = j
                if replaced_one not in final_list:
                    final_list.append(replaced_one)
                replaced_one = list_1[:]






    return final_list

print(replaced_it([1,2,3,4],7))

output:

[[7, 2, 3, 4], [1, 7, 3, 4], [1, 2, 7, 4], [1, 2, 3, 7], [7, 7, 3, 4], [7, 2, 7, 4], [7, 2, 3, 7], [1, 7, 7, 4], [1, 7, 3, 7], [1, 2, 7, 7], [7, 7, 7, 4], [7, 7, 3, 7], [7, 2, 7, 7], [1, 7, 7, 7], [7, 7, 7, 7]]