[R] unexpected 'else' in " else"
Jeff Newmiller
jdnewm|| @end|ng |rom dcn@d@v|@@c@@u@
Sat Oct 22 00:13:10 CEST 2022
Your selection priorities are inverted: ifelse is vectorised... use it to make many individual choices at once with a single atomic vector result. If-else is a control-flow construct... you can return one object of any type from it based on a single comparison or alter variables and ignore the return value (or both, though that is probably not going to make for clear readability). Their use cases might appear to overlap if you choose to work with a length-one vector, but that is a somewhat obscure mis-use of ifelse.
On October 21, 2022 10:38:48 AM PDT, "Ebert,Timothy Aaron" <tebert using ufl.edu> wrote:
>Is there a place where you would use ifelse()? I used it here because it was short and there was no indication of lots of data. In the example I cannot tell the difference of a few hundred milliseconds execution time. Benchmarking code is important for larger problems.
>
>Tim
>
>-----Original Message-----
>From: Martin Maechler <maechler using stat.math.ethz.ch>
>Sent: Friday, October 21, 2022 8:43 AM
>To: Ebert,Timothy Aaron <tebert using ufl.edu>
>Cc: Andrew Simmons <akwsimmo using gmail.com>; Jinsong Zhao <jszhao using yeah.net>; R-help Mailing List <r-help using r-project.org>
>Subject: Re: [R] unexpected 'else' in " else"
>
>[External Email]
>
>>>>>> Ebert,Timothy Aaron
>>>>>> on Fri, 21 Oct 2022 12:05:58 +0000 writes:
>
> > I can get it to work with
> > ifelse(is.matrix(r), r[w!=0, , drop=FALSE], r[w!=0])
>
>Note that this is *not* good advice:
>
> if(Cnd) A else B is very much more efficient than
> ifelse(Cnd, A, B)
>
>whenever it is appropriate, i.e.,
>the condition Cnd is a simple TRUE or FALSE.
>
>ifelse() is very much over-used!
>
>{For the more sophisticated reader:
> In R, these both are function calls:
> `if` is a function of 3 argument with a "peculiar" syntax and the third argument with default NULL.
>}
>
>Martin Maechler
>ETH Zurich and R Core team
>
>
>
> > With w and r as defined r is not a matrix, so the first part will never execute. The test is for w not equal to zero so it is always true for these vectors. It is usually good to have test code such that all possible cases are activated.
>
> > r<--1:8
> > w<- -1:5
> > if(is.matrix(r)){
> > r[w!=0, , drop=FALSE]
> > } else r[w != 0]
>
> > I think this also works. The "else" must follow the } and you put in a carriage return after the }
>
> > I think that is the answer, but not 100% sure.
>
> > Tim
>
> > -----Original Message-----
> > From: R-help <r-help-bounces using r-project.org> On Behalf Of Andrew Simmons
> > Sent: Friday, October 21, 2022 5:37 AM
> > To: Jinsong Zhao <jszhao using yeah.net>
> > Cc: R-help Mailing List <r-help using r-project.org>
> > Subject: Re: [R] unexpected 'else' in " else"
>
> > [External Email]
>
> > The error comes from the expression not being wrapped with braces. You could change it to
>
> > if (is.matrix(r)) {
> > r[w != 0, , drop = FALSE]
> > } else r[w != 0]
>
> > or
>
> > {
> > if (is.matrix(r))
> > r[w != 0, , drop = FALSE]
> > else r[w != 0]
> > }
>
> > or
>
> > if (is.matrix(r)) r[w != 0, , drop = FALSE] else r[w != 0]
>
>
> > On Fri., Oct. 21, 2022, 05:29 Jinsong Zhao, <jszhao using yeah.net> wrote:
>
> >> Hi there,
> >>
> >> The following code would cause R error:
> >>
> >> > w <- 1:5
> >> > r <- 1:5
> >> > if (is.matrix(r))
> >> + r[w != 0, , drop = FALSE]
> >> > else r[w != 0]
> >> Error: unexpected 'else' in " else"
> >>
> >> However, the code:
> >> if (is.matrix(r))
> >> r[w != 0, , drop = FALSE]
> >> else r[w != 0]
> >> is extracted from stats::weighted.residuals.
> >>
> >> My question is why the code in the function does not cause error?
> >>
> >> Best,
> >> Jinsong
> >>
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