R help - Dec 2019 - Having problems with the ifelse and negative numbers

Please consider the following two R statements:
     A =  runif(20, min=-1,max=1)
     ifelse( A < 0, sqrt(-A), A )

The second statement produces the following error message:
     rt(-A) : NaNs produced

I understand that you cannot take the square root of a negative number 
but I thought the condition A < 0
would take care of that issue. It appears not to be.

What am I missing?

Thanks,
Bob

The sqrt(-A) is evaluated for all A. The result returned is conditional on the
first argument but the other two arguments are evaluated on the entire vector.

Kevin

-- 
Kevin E. Thorpe
Head of Biostatistics,  Applied Health Research Centre (AHRC)
Li Ka Shing Knowledge Institute of St. Michael's
Assistant Professor, Dalla Lana School of Public Health
University of Toronto
email: kevin.thorpe at utoronto.ca  Tel: 416.864.5776  Fax: 416.864.3016
 

?On 2019-12-09, 7:58 AM, "R-help on behalf of rsherry8"
<r-help-bounces at r-project.org on behalf of rsherry8 at comcast.net>
wrote:

    Please consider the following two R statements:
         A =  runif(20, min=-1,max=1)
         ifelse( A < 0, sqrt(-A), A )
    
    The second statement produces the following error message:
         rt(-A) : NaNs produced
    
    I understand that you cannot take the square root of a negative number 
    but I thought the condition A < 0
    would take care of that issue. It appears not to be.
    
    What am I missing?
    
    Thanks,
    Bob
    
    ______________________________________________
    R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
    https://stat.ethz.ch/mailman/listinfo/r-help
    PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
    and provide commented, minimal, self-contained, reproducible code.

Hi Bob,
You wrote "the following error message" -
when in fact it is a Warning and not an error message. I think your
code does what you hoped it would do, in the sense it successfully
calculates the sqrt(abs(negativeNumber)), where appropriate.

If you want to run the code without seeing this warning message you can run

ifelse( A < 0, suppressWarnings(sqrt(-A)), A )

and you should be fine.

HTH,
Eric

On Mon, Dec 9, 2019 at 3:18 PM Kevin Thorpe <kevin.thorpe at utoronto.ca>
wrote:
>
> The sqrt(-A) is evaluated for all A. The result returned is conditional on
the first argument but the other two arguments are evaluated on the entire
vector.
>
> Kevin
>
> --
> Kevin E. Thorpe
> Head of Biostatistics,  Applied Health Research Centre (AHRC)
> Li Ka Shing Knowledge Institute of St. Michael's
> Assistant Professor, Dalla Lana School of Public Health
> University of Toronto
> email: kevin.thorpe at utoronto.ca  Tel: 416.864.5776  Fax: 416.864.3016
>
>
> ?On 2019-12-09, 7:58 AM, "R-help on behalf of rsherry8"
<r-help-bounces at r-project.org on behalf of rsherry8 at comcast.net>
wrote:
>
>     Please consider the following two R statements:
>          A =  runif(20, min=-1,max=1)
>          ifelse( A < 0, sqrt(-A), A )
>
>     The second statement produces the following error message:
>          rt(-A) : NaNs produced
>
>     I understand that you cannot take the square root of a negative number
>     but I thought the condition A < 0
>     would take care of that issue. It appears not to be.
>
>     What am I missing?
>
>     Thanks,
>     Bob
>
>     ______________________________________________
>     R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>     https://stat.ethz.ch/mailman/listinfo/r-help
>     PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
>     and provide commented, minimal, self-contained, reproducible code.
>
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.