ragged.R

library(data.table)
library(SOfun)

ragged <- function(indt, keys, blank = "") {
  require(data.table)
  indt <- setkeyv(as.data.table(indt), keys)
  vals <- setdiff(names(indt), keys)
  nams <- paste0(keys, "_copy")
  for (i in seq_along(nams)) {
    indt[, (nams[i]) := c(as.character(get(key(indt)[i])[1]),
                          rep(blank, .N-1)), by = eval(keys[seq(i)])]
  }
  out <- cbind(indt[, ..nams], indt[, ..vals])
  out <- setnames(out, nams, keys)[]
  out <- list(indt = indt[, (nams) := NULL][], out = out, keys = keys, blank = blank)
  class(out) <- c("ragged", class(out))
  out
}

print.ragged <- function(x, ...) {
  print(x$out)
}

`[.ragged` <- function(inragged, ...) {
  out <- inragged$indt[...]
  out <- ragged(out, keys = intersect(inragged$keys, names(out)), blank = inragged$blank)
  out
}

x <- xtabs(cbind(ncases, ncontrols) ~ ., data = esoph)
ragged(ftable2dt(x), c("agegp", "alcgp", "tobgp"), ".")