Re: [R] passing a modified argument to an S3 method
I've got a complicated default value for an argument, basically a "control"
argument that's a list with a lot of defaults, and I want to figure out its
value before dispatching to a method so I don't need to have the same code
repeated at the beginning of every method. None of the default values should be
method-dependent, so I don't need or want each method to figure out the value
separately. I hope that helps!
Jay
On Saturday, April 20th, 2024 at 10:51 AM, Bert Gunter
wrote:
> I do not understand what your goal is here (more context may be helpful,
> perhaps to others rather than me). So I doubt this is what you want, but here
> is a guess -- no need to respond if it is unhelpful:
>
> ## test.default returns NULL if object "y" not found in **calling environment
> and enclosures**;
> ## otherwise y.
>
> test <- function(x){
> UseMethod("test")
> }
> test.default <- function(x){
> tryCatch(y, error = function(e)NULL)
> }
>
> ## y not found
> test(x=3)
> NULL
>
> ## y found
> > y <- 'abcd'
> > test(x = 3)
> [1] "abcd"
>
> Cheers,
> Bert
>
>
>
>
> On Sat, Apr 20, 2024 at 4:23 AM CRAN.r via R-help
> wrote:
>
> > Is there a way to pass a modified argument from an S3 generic to a method?
> > Here's a non-working example that I want to return "abcd".
> >
> > test <- function(x, y = NULL){
> > y <- "abcd"
> > UseMethod("test")
> > }
> > test.default <- function(x, y = NULL) y
> > test(x = 3)
> >
> > Is that possible? I've looked around a lot, but can't find any examples or
> > discussion.
> >
> > Jay
> >
> > __
> > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > 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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Re: [R] passing a modified argument to an S3 method
> On Apr 19, 2024, at 1:36 PM, CRAN.r via R-help wrote:
>
> Is there a way to pass a modified argument from an S3 generic to a method?
> Here's a non-working example that I want to return "abcd".
>
grep-ing the source code is often a good way to answer a question like this.
Particularly, with NextMethod there seem to be plenty of instances in which the
original arguments are modified before a call to a method.
One such is `t.data.frame` and there seem to be other methods for "data.frame"
objects that modify the objects before calling NextMethod.
HTH,
Chuck
> test <- function(x, y = NULL){
>y <- "abcd"
>UseMethod("test")
> }
> test.default <- function(x, y = NULL) y
> test(x = 3)
>
> Is that possible? I've looked around a lot, but can't find any examples or
> discussion.
>
> Jay
>
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Re: [R] passing a modified argument to an S3 method
The parameters in a specific call to a function are stored in a special list
which is used to move/copy data from the calling environment into the
environment created for a particular function call.
UseMethod does not act like a normal function call... it does a kind of magic
substitution of the implementation method `test.default` into the call stack
where the generic function `test` was. The argument list remains, but the
environment associated with the generic function `test` is discarded in the
process. The argument list was never actually modified in `test`... just the
environment.
You are expected to think of `test` as a placeholder... a kind of abstract
method that doesn't actually do anything other than map from a generic method
to an implementation method. Your goal of adding shared behavior this way is
not possible.
I recommend reading Advanced R in book form or online to help you navigate R
behavior like this.
On April 20, 2024 8:51:23 AM PDT, Bert Gunter wrote:
>I do not understand what your goal is here (more context may be helpful,
>perhaps to others rather than me). So I doubt this is what you want, but
>here is a guess -- no need to respond if it is unhelpful:
>
>## test.default returns NULL if object "y" not found in **calling
>environment and enclosures**;
>## otherwise y.
>
>test <- function(x){
> UseMethod("test")
>}
>test.default <- function(x){
> tryCatch(y, error = function(e)NULL)
>}
>
>## y not found
>test(x=3)
>NULL
>
>## y found
>> y <- 'abcd'
>> test(x = 3)
>[1] "abcd"
>
>Cheers,
>Bert
>
>
>
>
>On Sat, Apr 20, 2024 at 4:23 AM CRAN.r via R-help
>wrote:
>
>> Is there a way to pass a modified argument from an S3 generic to a
>> method? Here's a non-working example that I want to return "abcd".
>>
>> test <- function(x, y = NULL){
>> y <- "abcd"
>> UseMethod("test")
>> }
>> test.default <- function(x, y = NULL) y
>> test(x = 3)
>>
>> Is that possible? I've looked around a lot, but can't find any examples or
>> discussion.
>>
>> Jay
>>
>> __
>> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> 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.
>>
>
> [[alternative HTML version deleted]]
>
>__
>R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
>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.
--
Sent from my phone. Please excuse my brevity.
__
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Re: [R] passing a modified argument to an S3 method
I do not understand what your goal is here (more context may be helpful,
perhaps to others rather than me). So I doubt this is what you want, but
here is a guess -- no need to respond if it is unhelpful:
## test.default returns NULL if object "y" not found in **calling
environment and enclosures**;
## otherwise y.
test <- function(x){
UseMethod("test")
}
test.default <- function(x){
tryCatch(y, error = function(e)NULL)
}
## y not found
test(x=3)
NULL
## y found
> y <- 'abcd'
> test(x = 3)
[1] "abcd"
Cheers,
Bert
On Sat, Apr 20, 2024 at 4:23 AM CRAN.r via R-help
wrote:
> Is there a way to pass a modified argument from an S3 generic to a
> method? Here's a non-working example that I want to return "abcd".
>
> test <- function(x, y = NULL){
> y <- "abcd"
> UseMethod("test")
> }
> test.default <- function(x, y = NULL) y
> test(x = 3)
>
> Is that possible? I've looked around a lot, but can't find any examples or
> discussion.
>
> Jay
>
> __
> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.
>
[[alternative HTML version deleted]]
__
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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.
