[R] Having problems with the ifelse and negative numbers
Marc Girondot
m@rc_grt @end|ng |rom y@hoo@|r
Tue Dec 10 10:27:59 CET 2019
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 à 19:25, Richard M. Heiberger a écrit :
> or even simpler
> sqrt(abs(A))
>
> On Mon, Dec 9, 2019 at 8:45 AM Eric Berger <ericjberger using 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 using 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 using 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 using r-project.org on behalf of rsherry8 using 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 using 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 using 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 using 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 using 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.
>
More information about the R-help
mailing list