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)
}

@MichaelChirico thank you for the notes. I hope we will look something like that in data.table.

🚀 i wonder lubridate would accept a PR... I don't see mem_alloc on your benchmark, but on mine it's 5x faster & 10x less memory... sacrifice is slight readability issue on internal code? can be solved with comments ideally

Strange to me there's no trunc.Date('week') method in base. Anyway, we might consider supporting that in trunc.IDate if you could please file PR 🙏

lubridate wants stringr...

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

Good idea. I'll do it.