See: http://stackoverflow.com/q/35456914/1270695

meltList.R

meltList <- function(inlist) {
  require(data.table)
  f <- function(l) {
    names(l) <- seq_along(l)
    lapply(l, function(x) {
      x <- setNames(x, seq_along(x))
      if(is.list(x)) f(x) else x
    })
  }
  temp <- unlist(f(inlist))
  setDT(tstrsplit(names(temp), ".", fixed = TRUE))[
    , value := unname(temp)][]
}