Description of the class "Date" representing calendar dates.
# S3 method for Date
summary(object, digits = 12, …)An object summarized.
Number of significant digits for the computations.
Further arguments to be passed from or to other methods.
Dates are represented as the number of days since 1970-01-01, with negative values for earlier dates. They are always printed following the rules of the current Gregorian calendar, even though that calendar was not in use long ago (it was adopted in 1752 in Great Britain and its colonies).
It is intended that the date should be an integer, but this is not
  enforced in the internal representation.  Fractional days will be
  ignored when printing.  It is possible to produce fractional days via
  the 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.