# [R] unexpected 'else' in " else"

Ebert,Timothy Aaron tebert @end|ng |rom u||@edu
Fri Oct 21 19:38:48 CEST 2022

```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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