Merge Two Lists in R

Question

I have two lists

first = list(a = 1, b = 2, c = 3) second = list(a = 2, b = 3, c = 4) 

I want to merge these two lists so the final product is

$a [1] 1 2  $b [1] 2 3  $c [1] 3 4 

Is there a simple function to do this?

Answer 1

If lists always have the same structure, as in the example, then a simpler solution is

mapply(c, first, second, SIMPLIFY=FALSE) 

Answer 2

This is a very simple adaptation of the modifyList function by Sarkar. Because it is recursive, it will handle more complex situations than mapply would, and it will handle mismatched name situations by ignoring the items in 'second' that are not in 'first'.

appendList <- function (x, val)  {     stopifnot(is.list(x), is.list(val))     xnames <- names(x)     for (v in names(val)) {         x[[v]] <- if (v %in% xnames && is.list(x[[v]]) && is.list(val[[v]]))              appendList(x[[v]], val[[v]])         else c(x[[v]], val[[v]])     }     x }  > appendList(first,second) $a [1] 1 2  $b [1] 2 3  $c [1] 3 4