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

Answer 1

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