Revert list structure

Question

GOAL

Given a list of lists my goal is to reverse its structure (R language).

So, I want to bring the elements of the nested lists to be el

Answer 1

How about this simple solution, which is completely general, and almost as fast as Josh O'Brien's original answer that assumed common internal names (#4).

zv <- unlist(unname(z), recursive=FALSE)
ans <- split(setNames(zv, rep(names(z), lengths(z))), names(zv))

And here is a general version that is robust to not having names:

invertList <- function(z) {
    zv <- unlist(unname(z), recursive=FALSE)
    zind <- if (is.null(names(zv))) sequence(lengths(z)) else names(zv)
    if (!is.null(names(z)))
        zv <- setNames(zv, rep(names(z), lengths(z)))
    ans <- split(zv, zind)
    if (is.null(names(zv))) 
        ans <- unname(ans)
    ans
}