How to make a for loop for each vector in list

Question

I have a list l, contains four vectors, each vector contains a number of elements, the vectors are not the same length.

l<- list(2:4,3:5,4:7,5:7)

  for ( i in length(l)){

     print(l)
   }

[[1]]
[1] 2 3 4

[[2]]
[1] 3 4 5

[[3]]
[1] 4 5 6 7

[[4]]
[1] 5 6 7

I would like to add value 2 to all the elements of each vector in the list using for loop.
Maybe we need ( two for loops ) The external will be for the list and the internal will be for each vector of the list, I would like to obtain the following result :

    [[1]]
    [1] 4 5 6

    [[2]]
    [1] 5 6 7

    [[3]]
    [1] 6 7 8 9

    [[4]]
    [1] 7 8 9

Please note that: the original list contains 389 vectors, each vector contains not less than 45 elements.

Answer 1

A much faster and cleaner way is to not use a loop. Here, we are mapping each vector .x in l to .x + 2 .

purrr::map(l, ~.x + 2)
# [[1]]
# [1] 4 5 6
# 
# [[2]]
# [1] 5 6 7
# 
# [[3]]
# [1] 6 7 8 9
# 
# [[4]]
# [1] 7 8 9

If you really need the loop version, just loop through the indexes of l and add 2 to each vector.

for (i in seq_along(l)) {
  l[[i]] <- l[[i]] + 2
}
print(l)
# [[1]]
# [1] 4 5 6
# 
# [[2]]
# [1] 5 6 7
# 
# [[3]]
# [1] 6 7 8 9
# 
# [[4]]
# [1] 7 8 9