How to make a list of integer vectors in R

Question

Basic question: In R, how can I make a list and later populate it with vector elements?

l <- list()  l[1] <- c(1,2,3)  

This gives the error "number of items to replace is not a multiple of replacement length", so R is trying to unpack the vector. The only way I have found to work so far is to add the vectors when making the list.

l <- list(c(1,2,3), c(4,5,6)) 

Answer 1

According to ?"[" (under the section "recursive (list-like) objects"):

 Indexing by ‘[’ is similar to atomic vectors and selects a list of  the specified element(s).   Both ‘[[’ and ‘$’ select a single element of the list.  The main  difference is that ‘$’ does not allow computed indices, whereas  ‘[[’ does.  ‘x$name’ is equivalent to ‘x[["name", exact =  FALSE]]’.  Also, the partial matching behavior of ‘[[’ can be  controlled using the ‘exact’ argument. 

Basically, for lists, [ selects more than one element, so the replacement must be a list (not a vector as in your example). Here's an example of how to use [ on lists:

l <- list(c(1,2,3), c(4,5,6)) l[1] <- list(1:2) l[1:2] <- list(1:3,4:5) 

If you only want to replace one element, use [[ instead.

l[[1]] <- 1:3 

Answer 2

Use [[1]] as in

l[[1]] <- c(1,2,3) l[[2]] <- 1:4 

and so. Also recall that preallocation is much more efficient, so if you know how long your list is going to be, use something like

l <- vector(mode="list", length=N)