[R] inconsistency in switch statements.....

[Bert Gunter]

Inline.

On Wed, Sep 7, 2022 at 12:18 PM akshay kulkarni <akshay_e4 using hotmail.com> wrote:
>
> Dear Bert,
>                     Thanks...I went through the doc pages but couldn't glean from that that for numeric options one has to backtick it.

That's because your statement is false. Perhaps you misstated what you
meant, but for numeric options, the match is **always** chosen by
position, whether or not the arguments are labeled, whether or not the
labels are backticked numerics or not.

> a <- 2
> switch(a, `44` = 'No', howdy_pardner = 'Yes')
[1] "Yes"
> a = 44 ## can't work with only two positional choices
> switch(a, `44` = 'No', howdy_pardner = 'Yes')
> ## No match, so none returned and printed as above

"I is not given in the doc page...I actually had hundreds of different
choices and so cannot depend on evaluation by position..."

.... which, to repeat, is false if choices evaluate to/can be coerced
to integers. Evaluation is *always* by position in that case.

> a <- 2.3
> switch(a, `44` = 'No', howdy_pardner = 'Yes')
[1] "Yes"
## because
> as.integer(2.3)
[1] 2

-- 
Bert

>
> Yours sincerely,
> AKSHAY M KULKARNI
>
> ________________________________
> From: Bert Gunter <bgunter.4567 using gmail.com>
> Sent: Thursday, September 8, 2022 12:39 AM
> To: akshay kulkarni <akshay_e4 using hotmail.com>
> Cc: R help Mailing list <r-help using r-project.org>
> Subject: Re: [R] inconsistency in switch statements.....
>
> Well, as it states on the Help page, which should always be the first
> place to look for, ummm, help:
>
> "If the value of EXPR is not a character string it is coerced to
> integer. Note that this also happens for factors, with a warning, as
> typically the character level is meant. If the integer is between 1
> and nargs()-1 then the corresponding element of ... is evaluated and
> the result returned: thus if the first argument is 3 then the fourth
> argument is evaluated and returned."
>
> So following up on Bill's comment, the arguments do not even need to
> be names when Stst evaluates to) an integer:
>
> > Stst <- 2
> > switch(Stst, print("NO"), print("YES"))
> [1] "YES"
>
> Cheers,
> Bert
>
> On Wed, Sep 7, 2022 at 11:35 AM akshay kulkarni <akshay_e4 using hotmail.com> wrote:
> >
> > Dear members,
> >                              The following is my code:
> >
> > > Stst <- 2
> > > switch(Stst, 1 = print("NO"), 2 = print("YES"))
> > Error: unexpected '=' in "switch(Stst, 1 ="
> >
> > Why isn't it printing "YES" on to the console?
> >
> > many thanks in advance.
> >
> > Thanking you,
> > Yours sincerely,
> > AKSHAY M KULKARNI
> >
> >         [[alternative HTML version deleted]]
> >
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