How to replace all list of list items with the index value of that list-CodePudding

I am trying to replace items in list of lists by the value of the index of that specific list. I can do it with a for loop, but I was wondering if there is a faster way to do this.

such that the following list

example = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

becomes:

solution = [[0, 0, 0], [1, 1, 1], [2, 2, 2]]

CodePudding user response：

Your way with for loop should work, but if you want another way in a short version then you can do it this way with list comprehension and enumerate,

example = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
result = [[index] * len(value) for index, value in enumerate(example)]
print(result)

CodePudding user response：

List comprehensions are usually faster than loops

Here is a solution with list comprehensions

example = [[1,2,3],[4,5,6],[7,8,9]]
solution = [[x for _ in range(len(example[x]))] for x in range(len(example))]
print(solution)

Output
[[0, 0, 0], [1, 1, 1], [2, 2, 2]]

CodePudding user response：

solution = [[i]*len(x) for i, x in enumerate(example)]

CodePudding user response：

Here is a solution with the map function:

res = list(map(lambda i : [i] * len(example[i]),
            range(len(example))
        ))
print(res)

It's more verbose than the comprehension method, but coming from other languages I prefer it - I find the map to be more explicit and easier to follow, as it's built out of the common components of higher-order functions rather than having its own syntax.