Date Class

Description

Description of the class "Date" representing calendar dates.

Usage

## S3 method for class 'Date'
summary(object, digits = 12, ...)

## S3 method for class 'Date'
print(x, max = NULL, ...)

Arguments

Details

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). When printing there is assumed to be a year zero.

It is intended that the date should be an integer value, 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).

When a date is converted to a date-time (for example by as.POSIXct or as.POSIXlt its time is taken as midnight in UTC.

Printing dates involves conversion to class "POSIXlt" which treats dates of more than about 780 million years from present as NA.

For the many methods see methods(class = "Date"). Several are documented separately, see below.

Warning

Do not use identical() on objects of class "Date". Their storage.mode may be "dpuble" or "integer", and which is chosen has depended on the version of R used to create the object.

See Also

Sys.Date for the current date.

weekdays for convenience extraction functions.

Methods with extra arguments and documentation:

Ops.Date

for operators on "Date" objects.

format.Date

for conversion to and from character strings.

axis.Date

and hist.Date for plotting.

seq.Date

, cut.Date, and round.Date for utility operations.

DateTimeClasses for date-time classes.

Examples

(today <- Sys.Date())
format(today, "%d %b %Y")  # with month as a word
(tenweeks <- seq(today, length.out=10, by="1 week")) # next ten weeks
weekdays(today)
months(tenweeks)

(Dls <- as.Date(.leap.seconds))

## Show use of year zero:
(z <- as.Date("01-01-01")) # how it is printed depends on the OS
z - 365 # so year zero was a leap year.
as.Date("00-02-29")
# if you want a different format, consider something like (if supported)
## Not run: format(z, "%04Y-%m-%d") # "0001-01-01"
format(z, "%_4Y-%m-%d") # "   1-01-01"
format(z, "%_Y-%m-%d")  # "1-01-01"

## End(Not run) 

##  length(<Date>) <- n   now works
ls <- Dls; length(ls) <- 12
l2 <- Dls; length(l2) <- 5 + length(Dls)
stopifnot(exprs = {
  ## length(.) <- * is compatible to subsetting/indexing:
  identical(ls, Dls[seq_along(ls)])
  identical(l2, Dls[seq_along(l2)])
  ## has filled with NA's
  is.na(l2[(length(Dls)+1):length(l2)])
})