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Eric Berger

2019-Dec-09 13:44 UTC

[R] 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 <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.

Richard M. Heiberger

2019-Dec-09 18:25 UTC

head link

[R] Having problems with the ifelse and negative numbers

or even simpler
sqrt(abs(A))

On Mon, Dec 9, 2019 at 8:45 AM Eric Berger <ericjberger at gmail.com>
wrote:>
> 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.
>
> ______________________________________________
> 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.

Marc Girondot

2019-Dec-10 09:27 UTC

head link

[R] Having problems with the ifelse and negative numbers

Here is a test of the different proposed solutions and a new one faster. 
In conclusion, ifelse much be used with caution:

Aini =? runif(1000000, min=-1,max=1)
library(microbenchmark)
A <- Aini
microbenchmark({B1 <- ifelse( A < 0, sqrt(-A), A )})
# mean = 77.55551
A <- Aini
microbenchmark({B2 <- ifelse( A < 0, suppressWarnings(sqrt(-A)), A )})
# mean = 76.53762
A <- Aini
microbenchmark({B3 <- ifelse( A < 0, sqrt(abs(A)), A )})
# mean = 75.26712
A <- Aini
microbenchmark({A[A < 0] <- sqrt(-A[A < 0]);B4 <- A})
# mean = 17.71883

Marc

Le 09/12/2019 ? 19:25, Richard M. Heiberger a ?crit?:> or even simpler
> sqrt(abs(A))
>
> On Mon, Dec 9, 2019 at 8:45 AM Eric Berger <ericjberger at gmail.com>
wrote:
>> 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.
>> ______________________________________________
>> 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.
>

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

[R] Having problems with the ifelse and negative numbers

[R] Having problems with the ifelse and negative numbers

[R] Having problems with the ifelse and negative numbers