Floor dates function

floor_date.R

#' @title Floor Dates
#' @param x A vector of date.
#' @param unit A character string specifying a time unit.
#' @param start.on.monday Should the week start on Mondays or Sundays?
#' @return An object of class "Date".
floor_date <- function(x, unit = c("day", "week", "month", "quarter", "year"), start.on.monday = TRUE) {
  stopifnot(is(x, "Date"))
  unit <- match.arg(unit)
  if (unit == "day") {
    return(x)
  }
  if (unit == "week") {
    l <- ((unclass(ll) - 3L) %/% 7L) * 7L + 4L
    if (start.on.monday) {
      return(.Date(7 * ((unclass(x) - 4L) %/% 7) + 4L))
    } else {
      return(.Date(7 * ((unclass(x) - 3L) %/% 7) + 3L))
    }
  } else {
    l <- as.POSIXlt(x)
    l <- switch(
      unit,
      month = l$mday,
      quarter = l$mon %/% 3L,
      year = l$year
    )
  }
  return(x - l + 1L)
}

Anyway, we might consider supporting that in trunc.IDate if you could please file PR pray

Good idea. I'll do it.