date.object {survival} | R Documentation |
Objects of class "date"
.
is.date(x)
x |
any R object. |
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.
is.date
returns TRUE
if x
has class
"date"
, and FALSE
otherwise. Its behavior is unaffected
by any attributes of x
; for example, x
could be a date
array (in contrast to the behavior of is.vector
).
as.date
returns x
if x
is a simple object of
class "date"
, and otherwise a date vector of the same length as
x
and with data resulting from coercing the elements of
x
to class "date"
. See the manual page for
as.date()
for details.
Logical operations as well as the numeric functions exp()
,
log()
, and so on are invalid.
Other methods exist for missing value, as.character()
,
printing, and summarizing.
date.mdy
,
mdy.date
,
date.ddmmmyy
,
as.date
.