# [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
>>>      and provide commented, minimal, self-contained, reproducible code.
>>>
>>>
>>> ______________________________________________
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>>> and provide commented, minimal, self-contained, reproducible code.
>> ______________________________________________
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