Use global positions to mutate list, in list of lists

I need to keep my data in a list of lists, but want to edit elements in the lists based on their overall position.

For instance:

mylist = [['h','e','l','l','o'], ['w','o','r','l','d']]

I want to change position 5 as if it was all one list resulting in:

[['h','e','l','l','o'], ['change','o','r','l','d']]

This is for very large lists and lots of mutations so speed is essential!

Answer

Here is the solution of your’s question

# initializing list
input_list = [['h', 'e', 'l', 'l', 'o'], ['w', 'o', 'r', 'l', 'd']]

print("The initial list is : " + str(input_list))

length: int = 0

# define position(global index) where you want to update items in list
change_index = 5

## global starting index of sublist [0,5]
sub_list_start_index: list = list()

for sub_list in input_list:
    sub_list_start_index.append(length)
    length += len(sub_list)

    # check if index we want to change is <= global list index and
    if change_index <= length - 1 and change_index >= max(sub_list_start_index):
        sub_list_index = int(change_index - max(sub_list_start_index))
        input_list[input_list.index(sub_list)][sub_list_index] = 'change'

print("Updated list : " + str(input_list))

Output:

The initial list is : [['h', 'e', 'l', 'l', 'o'], ['w', 'o', 'r', 'l', 'd']]
Updated list : [['h', 'e', 'l', 'l', 'o'], ['change', 'o', 'r', 'l', 'd']]