R/excel_to_date.R

In dttr2: Manipulate Date, POSIXct and hms Vectors

#' Convert Excel dates to dates.
#'
#' Converts Excel dates encoded as serial numbers to date class.
#'
#' @details Defaults to the modern Excel date encoding system. Excel for Mac
#' 2008 and earlier Mac versions of Excel use a different date system. If the
#' date 2016-01-01 is represented by 42370, it's the modern system. If it's
#' 40908, it's the old system.
#'
#' @inheritParams params
#' @param x A vector of numbers to convert.
#' @param modern A flag specifying whether to use the modern or old Excel date
#'   system.
#'
#' @return A floored Date vector.
#' @family floor
#' @export
#'
#' @examples
#' dtt_excel_to_date(42370)
#' dtt_excel_to_date(40908, modern = FALSE)
dtt_excel_to_date <- function(x, modern = TRUE, ...) {
  chk_unused(...)
  chk_flag(modern)
  chk_numeric(x)
  origin <- if (modern) as.Date("1899-12-30") else as.Date("1904-01-01")
  dtt_date(x, origin = origin)
}