Still confused about classes

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Hi Russ,

One tool that might help could be ?methods and ?showMethods

For example:
## for S3
methods(class = "Date")
## for S4
showMethods(classes = "Date")

regarding getting the actual year, I would use (though there may be
better ways):

format.Date(as.Date("2010-01-01"), format = "%Y")

HTH,

Josh
Hi,

I'm still confused about how to find out what methods are defined for a
given class. ?For example, I know that

today <- Sys.Date()
will produce an object of type Date. But I'm not sure what I can do with
Date objects or how I can find out.

?Date

refers me to the Date documentation page. But it doesn't tell me how, for
example, to extract the current year from a date object.

I tried

year(today)Error: could not find function "year"

Is there some other function that does the job? I want a function f such
that ? ?> f(today) ? ?will return 2011. Perhaps there is no such function.
?But in general I don't have any confidence that I would know how to find it
if it existed or that I would know how to assure myself that there was no
such function.

Thanks.

*-- Russ *

? ? ? ?[[alternative HTML version deleted]]

______________________________________________
R-help at r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/
See ?months.

methods(class = "Date")

would have got you there.

(Date is not an S4 class, so people should not be setting S4 methods 
on it without very good reason, and there are none in R itself.)

Hi Russ,

One tool that might help could be ?methods and ?showMethods

For example:
## for S3
methods(class = "Date")
## for S4
showMethods(classes = "Date")

regarding getting the actual year, I would use (though there may be
better ways):

format.Date(as.Date("2010-01-01"), format = "%Y")
Call format(), not its methods, or use strftime() directly.
HTH,

Josh

On Thu, Apr 28, 2011 at 11:05 PM, Russ Abbott <russ.abbott at gmail.com> wrote:
Hi,

I'm still confused about how to find out what methods are defined for a
given class. ?For example, I know that

today <- Sys.Date()
will produce an object of type Date. But I'm not sure what I can do with
Date objects or how I can find out.

?Date

refers me to the Date documentation page. But it doesn't tell me how, for
example, to extract the current year from a date object.

I tried

year(today)Error: could not find function "year"

Is there some other function that does the job? I want a function f such
that ? ?> f(today) ? ?will return 2011. Perhaps there is no such function.
?But in general I don't have any confidence that I would know how to find it
if it existed or that I would know how to assure myself that there was no
such function.

Thanks.

*-- Russ *

? ? ? ?[[alternative HTML version deleted]]

______________________________________________
R-help at r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/

______________________________________________
R-help at r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595
The function for getting the year from date  is there in package
lubridate (as well as many other convenient functions to work with
dates).

More generally, finding "all" methods for a given class may be a
little tricky. If "all" means everything you have installed and
currently attached to your search path then methods(class="Date") will
do it (for S3 classes). (but "The functions listed are  those which
_are named like methods_ and may not actually be   methods (known
exceptions are discarded in the code). ") The result depends on which
packages you have loaded: in my currently open R session,
methods("Date") lists 36 "possible methods" but after library(zoo) I
get two more ( "as.yearmon.Date" and "as.yearqtr.Date").

Regards,
Kenn
Hi,

I'm still confused about how to find out what methods are defined for a
given class. ?For example, I know that

today <- Sys.Date()
will produce an object of type Date. But I'm not sure what I can do with
Date objects or how I can find out.

?Date

refers me to the Date documentation page. But it doesn't tell me how, for
example, to extract the current year from a date object.

I tried

year(today)Error: could not find function "year"

Is there some other function that does the job? I want a function f such
that ? ?> f(today) ? ?will return 2011. Perhaps there is no such function.
?But in general I don't have any confidence that I would know how to find it
if it existed or that I would know how to assure myself that there was no
such function.

Thanks.

*-- Russ *

? ? ? ?[[alternative HTML version deleted]]

______________________________________________
R-help at r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

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