[R] Different output for "if else" and "ifelse" that I don't understand

[Bert Gunter]

Typo: last line should be

Even better, use
  p3p <- tryCatch(list(...), error=function(e) list())


Cheers,

Bert


Bert Gunter

"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Fri, Apr 28, 2017 at 8:34 AM, William Dunlap via R-help
<r-help at r-project.org> wrote:
> ifelse's vectorization messes this up.
>
> You could replace your original
>   if (class(try(list(...), silent=TRUE))=="try-error") p3p <- list() else
> p3p <- list(...)
> with
>   p3p <- if (class(try(list(...), silent=TRUE))=="try-error") list() else
> list(...)
> instead of using ifelse, since the return value of 'if ... else ...' is the
> value of whichever branch was taken.
>
> Even better, use
>   p3p <- try(list(...), error=function(e) list())
>
>
> Bill Dunlap
> TIBCO Software
> wdunlap tibco.com
>
> On Fri, Apr 28, 2017 at 2:21 AM, Marc Girondot via R-help <
> r-help at r-project.org> wrote:
>
>> Dear list-members,
>>
>> During the test phase of a function, I run it interactively (in Rstudio)
>> and the ... produces an error. Then I use this to read it:
>>
>> if (class(try(list(...), silent=TRUE))=="try-error") p3p <- list() else
>> p3p <- list(...)
>>
>> It works fine; interactively I will get
>>
>> > if (class(try(list(...), silent=TRUE))=="try-error") p3p <- list() else
>> p3p <- list(...)
>> > p3p
>> list()
>>
>> and within a function I will get a list with the ... value. Perfect.
>>
>> I wanted to simplify the line by doing:
>>
>> p3p <- ifelse(class(try(list(...), silent=TRUE))=="try-error", list(),
>> list(...))
>>
>> In interactive mode, it works but within a function, I don't get the names
>> of the parameters. I don't understand the logic behind this difference.
>> Have you an idea ?
>>
>> Thanks
>>
>> Marc
>>
>>
>> > Try1 <- function(...) {
>> +   if (class(try(list(...), silent=TRUE))=="try-error") p3p <- list()
>> else p3p <- list(...)
>> +   return(p3p)
>> + }
>> > Try1(k=100)
>> $k
>> [1] 100
>>
>> > Try1()
>> list()
>> > Try2 <- function(...) {
>> +   p3p <- ifelse(class(try(list(...), silent=TRUE))=="try-error", list(),
>> list(...))
>> +   return(p3p)
>> + }
>> > Try2(k=100)
>> [[1]]
>> [1] 100
>>
>> > Try2()
>> [[1]]
>> NULL
>>
>> ______________________________________________
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>> ng-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
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>
> ______________________________________________
> 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.