R help - Jun 2006 - evaluation of the alternative expression in ifelse

Dear all,

I am trying to avoid the warnings produced by:
> x <- -2:2
> log(x)
[1]       NaN       NaN      -Inf 0.0000000 0.6931472
Warning message:
production de NaN in: log(x)

I thought that using ifelse would be a solution, but it is not the case:
> ifelse(test = x < 0, yes = NaN, no = log(x))
[1]       NaN       NaN      -Inf 0.0000000 0.6931472
Warning message:
production de NaN in: log(x)

I am aware of the section "Warning" of the help page for ifelse:
Sometimes it is better to use a construction such as (tmp <- yes;
tmp[!test] <- no[!test]; tmp), possibly extended to handle missing
values in test.

However, is there a way to avoid the evaluation of the alternative
expression in ifelse when the argument test is false ?

Best regards,

Renaud
-- 
Renaud LANCELOT
D?partement Elevage et M?decine V?t?rinaire (EMVT) du CIRAD
Directeur adjoint charg? des affaires scientifiques

CIRAD, Animal Production and Veterinary Medicine Department
Deputy director for scientific affairs

Campus international de Baillarguet
TA 30 / B (B?t. B, Bur. 214)
34398 Montpellier Cedex 5 - France
T?l   +33 (0)4 67 59 37 17
Secr. +33 (0)4 67 59 39 04
Fax   +33 (0)4 67 59 37 95

Quoting Renaud Lancelot <renaud.lancelot at gmail.com>:
> Dear all,
> 
> I am trying to avoid the warnings produced by:
> 
> > x <- -2:2
> > log(x)
> [1]       NaN       NaN      -Inf 0.0000000 0.6931472
> Warning message:
> production de NaN in: log(x)
> 
> I thought that using ifelse would be a solution, but it is not the
> case:
> 
> > ifelse(test = x < 0, yes = NaN, no = log(x))
> [1]       NaN       NaN      -Inf 0.0000000 0.6931472
> Warning message:
> production de NaN in: log(x)
> 
> I am aware of the section "Warning" of the help page for ifelse:
> Sometimes it is better to use a construction such as (tmp <- yes;
> tmp[!test] <- no[!test]; tmp), possibly extended to handle missing
> values in test.
> 
> However, is there a way to avoid the evaluation of the alternative
> expression in ifelse when the argument test is false ?
I think the answer is no; the Details section of ifelse() reads: 

"... 'yes' will be evaluated if and only if *any* element of test
is
true, and analogously for 'no'." 

check also the code behind ifelse(). If you really want to use ifelse
(), then you could consider something like:

x <- -2:2
opt <- options(warn = -1)
ifelse(test = x < 0, yes = NaN, no = log(x))
options(opt)


I hope it helps.

Best,
Dimitris

> Best regards,
> 
> Renaud
> -- 
> Renaud LANCELOT
> D?partement Elevage et M?decine V?t?rinaire (EMVT) du CIRAD
> Directeur adjoint charg? des affaires scientifiques
> 
> CIRAD, Animal Production and Veterinary Medicine Department
> Deputy director for scientific affairs
> 
> Campus international de Baillarguet
> TA 30 / B (B?t. B, Bur. 214)
> 34398 Montpellier Cedex 5 - France
> T?l   +33 (0)4 67 59 37 17
> Secr. +33 (0)4 67 59 39 04
> Fax   +33 (0)4 67 59 37 95
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
> http://www.R-project.org/posting-guide.html
> 
> 

Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm

Try:

log(ifelse(x < 0, NaN, x))

or

suppressWarnings(ifelse(x < 0, NaN, log(x)))

or

ifelse(x < 0, NaN, log(pmax(0, x)))



On 6/4/06, Renaud Lancelot <renaud.lancelot at gmail.com>
wrote:
> Dear all,
>
> I am trying to avoid the warnings produced by:
>
> > x <- -2:2
> > log(x)
> [1]       NaN       NaN      -Inf 0.0000000 0.6931472
> Warning message:
> production de NaN in: log(x)
>
> I thought that using ifelse would be a solution, but it is not the case:
>
> > ifelse(test = x < 0, yes = NaN, no = log(x))
> [1]       NaN       NaN      -Inf 0.0000000 0.6931472
> Warning message:
> production de NaN in: log(x)
>
> I am aware of the section "Warning" of the help page for ifelse:
> Sometimes it is better to use a construction such as (tmp <- yes;
> tmp[!test] <- no[!test]; tmp), possibly extended to handle missing
> values in test.
>
> However, is there a way to avoid the evaluation of the alternative
> expression in ifelse when the argument test is false ?
>
> Best regards,
>
> Renaud
> --
> Renaud LANCELOT
> D?partement Elevage et M?decine V?t?rinaire (EMVT) du CIRAD
> Directeur adjoint charg? des affaires scientifiques
>
> CIRAD, Animal Production and Veterinary Medicine Department
> Deputy director for scientific affairs
>
> Campus international de Baillarguet
> TA 30 / B (B?t. B, Bur. 214)
> 34398 Montpellier Cedex 5 - France
> T?l   +33 (0)4 67 59 37 17
> Secr. +33 (0)4 67 59 39 04
> Fax   +33 (0)4 67 59 37 95
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html
>