Message-ID: <51DEABB4.7060409@gmail.com>
Date: 2013-07-11T12:57:24Z
From: Duncan Murdoch
Subject: does subset.data.frame need to accept extra arguments?
In-Reply-To: <CABdHhvFxZ13LfhHUbYPsMVSaSCvfE6zz9kLEx628i+0ZTv4QSA@mail.gmail.com>
On 13-07-11 12:59 PM, Hadley Wickham wrote:
>> It needs to have ... in the formal argument list because the generic
>> subset() does.
>>
>> It could enforce a run-time warning that some arguments were being skipped
>> (by testing length(list(...)) for example), but then NextMethod might fail,
>> in a case where an object has a complicated class vector.
>
> That wouldn't be a problem if the check was implemented in
> subset.data.frame, would it?
Suppose the class vector is c("myclass", "data.frame"). Then
subset.myclass would be called first if it existed. It might do some
simple computation and then use NextMethod. It should not need to know
that it is calling subset.data.frame next, so it will pass all of its
arguments along, possibly including some that subset.data.frame should
ignore.
Duncan Murdoch