[R] Still confused about classes

[Prof Brian Ripley]

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.)

On Thu, 28 Apr 2011, Joshua Wiley wrote:

> 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