[R] How to use ifelse without invoking warnings

[Avi Gross]

Ravi,

I have no idea what motivated the people who made ifelse() but there is no
reason they felt the need to program it to meet your precise need. As others
have noted, it probably was built to handle simple cases well and it expects
to return a result that is the same length as the input. If some of the
processing returns an NA or a NaN then that is what it probably should
return. 

What is the alternative? Return a shorter result? Replace it with a zero?
Fail utterly and abort the program?

YOU as the programmer should make such decisions for a non-routine case.

You can create functions with names like wrapperIf() and wrapperElse() and
do your ifelse like this:

result <- ifelse(condition, wrapperIf(args), wrapperElse(args))

Why the wrappers? If your logic is to replace NaN with 0 or NA or 666 or
Inf, then the code for it would invoke your functionality and if tested to
be a NaN it would replace it as you wish. Yes, it would slow things down a
bit but leave the ifelse() routine fairly simple.

If your goal is to remove those entries, you can do it after by manipulating
"result" above such as not keeping any item that matches 666, or even
without the wrappers, something like:

result <- result[!is.nan(result)]

But, of course, warnings are only suppressed if done right. Clearly you can
very selectively suppress warnings in the wrapper functions above without
also suppressing some other more valid warnings. But if the warning is
coming from ifelse() itself then not ever having it see a NaN would suppress
that.

Do note that the implementation of ifelse() is currently a function, not
some internal call. You can copy that and make your own slightly modified
version if you wish. 

(no R) Avi

-----Original Message-----
From: R-help <r-help-bounces using r-project.org> On Behalf Of Ravi Varadhan via
R-help
Sent: Friday, October 8, 2021 8:22 AMiu
To: John Fox <jfox using mcmaster.ca>l
Cc: R-Help <r-help using r-project.org>
Subject: Re: [R] How to use ifelse without invoking warnings

Thank you to Bert, Sarah, and John. I did consider suppressing warnings, but
I felt that there must be a more principled approach.  While John's solution
is what I would prefer, I cannot help but wonder why `ifelse' was not
constructed to avoid this behavior.

Thanks & Best regards,
Ravi
________________________________
From: John Fox <jfox using mcmaster.ca>
Sent: Thursday, October 7, 2021 2:00 PM
To: Ravi Varadhan <ravi.varadhan using jhu.edu>
Cc: R-Help <r-help using r-project.org>
Subject: Re: [R] How to use ifelse without invoking warnings


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Dear Ravi,

It's already been suggested that you could disable warnings, but that's
risky in case there's a warning that you didn't anticipate. Here's a
different approach:

 > kk <- k[k >= -1 & k <= n]
 > ans <- numeric(length(k))
 > ans[k > n] <- 1
 > ans[k >= -1 & k <= n] <- pbeta(p, kk + 1, n - kk, lower.tail=FALSE)  >
ans [1] 0.000000000 0.006821826 0.254991551 1.000000000

BTW, I don't think that you mentioned that p = 0.3, but that seems apparent
from the output you showed.

I hope this helps,
  John

--
John Fox, Professor Emeritus
McMaster University
Hamilton, Ontario, Canada
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On 2021-10-07 12:29 p.m., Ravi Varadhan via R-help wrote:
> Hi,
> I would like to execute the following vectorized calculation:
>
>    ans <- ifelse (k >= -1 & k <= n, pbeta(p, k+1, n-k, lower.tail = 
> FALSE), ifelse (k < -1, 0, 1) )
>
> For example:
>
>
>> k <- c(-1.2,-0.5, 1.5, 10.4)
>> n <- 10
>> ans <- ifelse (k >= -1 & k <= n, pbeta(p,k+1,n-k,lower.tail=FALSE), 
>> ifelse (k < -1, 0, 1) )
> Warning message:
> In pbeta(p, k + 1, n - k, lower.tail = FALSE) : NaNs produced
>> print(ans)
> [1] 0.000000000 0.006821826 0.254991551 1.000000000
>
> The answer is correct.  However, I would like to eliminate the annoying
warnings.  Is there a better way to do this?
>
> Thank you,
> Ravi
>
>
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>
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