TITLE(is.date @@ Date Objects )
Tests for objects of class LANG("date").
USAGE(
is.date(x)
as.date(x)
)
ARGUMENTS(
ARG(x@@)
any S-PLUS object.
)
PARA BOLD(VALUE)
LANG(is.date) returns LANG(TRUE) if LANG(x) has mode
LANG("date"), and
LANG(FALSE) otherwise.
Its behavior is unaffected by any attributes of LANG(x); for example, LANG(x) could
be a date array (in contrast to the behavior of LANG(is.vector)).

LANG(as.date) returns LANG(x) if LANG(x) is a simple object of mode LANG("date"), and
otherwise a date vector of the same length as LANG(x) and with data resulting
from coercing the elements of LANG(x) to mode LANG("date").   See the manual page
for as.date for details.
Dates are stored as the number of days since 1/1/1960, and are kept in
integer format.  (This is the same baseline value as is used by SAS).
The numerical methods for dates treat date-date as a numeric, and
date +- numeric as a date.
Logical operations as well as the numeric functions exp(), log(), and etc
are invalid.
Other methods exist for missing value, as.character, and printing.
PARA BOLD(SEE ALSO)
LANG(date.mdy), LANG(mdy.date), LANG(date.ddmmmyy), LANG(print.date), LANG(as.date), LANG(plot.date).
PARA ITALIC(File automatically converted from S(-PLUS) help format)
