date.object             package:survival             R Documentation

Date Objects

Description:

     Objects of class '"date"'.

Usage:

     is.date(x)

Arguments:

       x: any R object.

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.

     '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.

See Also:

     'date.mdy', 'mdy.date', 'date.ddmmmyy',  'as.date'.

