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CRAN.r

2024-Apr-19 20:36 UTC

[R] passing a modified argument to an S3 method

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

Bert Gunter

2024-Apr-20 15:51 UTC

head link

[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 <r-help at
r-project.org>
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 at 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.
>
	[[alternative HTML version deleted]]

Berry, Charles

2024-Apr-20 17:29 UTC

head link

[R] passing a modified argument to an S3 method

> On Apr 19, 2024, at 1:36?PM, CRAN.r via R-help <r-help at
r-project.org> 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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> 
> 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
>

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