# Having problems with the ifelse and negative numbers

5 messages
Open this post in threaded view
|

## 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 ______________________________________________ [hidden email] mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.
Open this post in threaded view
|

## Re: Having problems with the ifelse and negative numbers

 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: [hidden email]  Tel: 416.864.5776  Fax: 416.864.3016   ﻿On 2019-12-09, 7:58 AM, "R-help on behalf of rsherry8" <[hidden email] on behalf of [hidden email]> 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         ______________________________________________     [hidden email] 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.     ______________________________________________ [hidden email] mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.
Open this post in threaded view
|

## Re: Having problems with the ifelse and negative numbers

 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 <[hidden email]> 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: [hidden email]  Tel: 416.864.5776  Fax: 416.864.3016 > > > ﻿On 2019-12-09, 7:58 AM, "R-help on behalf of rsherry8" <[hidden email] on behalf of [hidden email]> 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 > >     ______________________________________________ >     [hidden email] 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. > > > ______________________________________________ > [hidden email] 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. ______________________________________________ [hidden email] mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.