"Date" representing calendar dates.# S3 method for Date
summary(object, digits = 12, …)mean method or by adding or subtracting (see
  Ops.Date). The print methods respect options("max.print").Sys.Date for the current date. Ops.Date for operators on "Date" objects. format.Date for conversion to and from character strings. axis.Date and
  hist.Date for plotting. weekdays for convenience extraction functions. seq.Date, cut.Date,
  round.Date for utility operations. DateTimeClasses for date-time classes.