`as.data.table` but adding in `names` from named `list` columns.

ASDT.R

library(data.table)

## Sample data
L <- list(A = 1:2, B = NULL, C = 3:4)
DF <- data.frame(ID = 1:3, V1 = I(L), V2 = I(unname(L)), V3 = I(setNames(L, c("X", "Y", "Z"))))
DF2 <- data.frame(ID = 1:3, V1 = letters[1:3], V2 = letters[4:6], V3 = letters[7:9])
DF3 <- do.call(rbind, replicate(1000, DF, FALSE))

set.seed(1)
DF4 <- data.frame(ID = 1:300000, V1 = I(rep(L, 100000)), V2 = I(rep(unname(L), 100000)),
                  V3 = I(setNames(rep(L, 100000), sample(c(LETTERS, letters), 300000, TRUE))))

ASDT <- function(input, keep.rownames = FALSE) {
  if (!is.list(input)) stop("ASDT is only for lists, data.frames, and data.tables")
  if (is.data.table(input)) {
    output <- input
  } else {
    if (!is.data.frame(input)) {
      input <- setNames(data.frame(I(input)), deparse(substitute(input)))
    }
    output <- as.data.table(input, keep.rownames = keep.rownames)
    lsts <- vapply(input, is.list, logical(1L))
    if (any(lsts)) {
      namd <- vapply(input[lsts], function(x) !is.null(names(x)), logical(1L))
      tofix <- names(namd)[namd]
      for (i in tofix) {
        set(output, j = sprintf("%s_names", i), value = names(input[[i]]))
      }
    }
  }
  output[]
}