Lists inside list, how to access elements?

Question

I have a function that needs to return two two different types of groups of vectors. I could do this using a list consisting of two matrices, where the vectors, that I want to return, correspond to columns in the matrix, but since the vectors all have different lengths, I would like to save the vectors in a list themselves, so that I have a list consisting of two lists.

I would like to add the vectors to the sublists now, but don't know which indices to use.

For example if I would like to add the vector x to the first sublist in my list(call it l), how would I do that?

l[[1]] <- x

would only replace the first vector in the first sublist, but how could I access the second element in the sublist using indices?

Answer 1

To add elements to sublists, start with the list:

l <- list(list(1:3), list(5:8))             
str(l)

Which looks like so:

List of 2
 $ :List of 1
  ..$ : int [1:3] 1 2 3
 $ :List of 1
  ..$ : int [1:4] 5 6 7 8

And add another vector inside a list:

l[[1]] <- c(l[[1]], list(100:103))
str(l)

Produces:

List of 2
 $ :List of 2
  ..$ : int [1:3] 1 2 3
  ..$ : int [1:4] 100 101 102 103
 $ :List of 1
  ..$ : int [1:4] 5 6 7 8