Question

I would like to ask if it is possible to add an element into a list.
For example the list

L <- vector("list", 2)
L[[1]] <- vector("list", 2)

I want to become

[[1]]
[[1]][[1]]
NULL

[[1]]            # add an element and it becomes [[1]]
[[1]][[2]]                                       [[1]][[2]][[3]]
NULL                                             NULL  

[[2]]
NULL

Thank you all, in advance

Answer 1

In your code for list “L”,

[[1]]
[[1]][[1]]

represents the first item in list [[1]] and can be referenced by L[[1]][[1]].

[[1]]
[[1]][[2]]

represents the second item in [[1]] and can be referenced by L[[1]][[2]]. So, to add a new element into the list, you can just use:

L[[1]][[3]] <- vector()

Personally, I find it much easier to work with named elements though, since keeping track of those brackets can be somewhat tedious.