R help - Apr 2016 - Problem with <= (less than or equal): not giving the expected result

Dear All,

I have the following problem:

I have a function in which I check if the difference between values is smaller
or equal to a certain threshold. I however realized that I might get there some
unexpected results:
> abs(1 - 0.95) >= 0.05
[1] TRUE
## So that?s fine, but:
> abs(1 - 0.95) <= 0.05
[1] FALSE

Apparently, abs(1 - 0.95) is not equal to 0.05, which I find however quite
disturbing.

Along these lines:
> abs(0.95 - 1) > 0.05
[1] TRUE
> abs(0.95 - 1) < 0.05
[1] FALSE

I guess that has to do with the floating point representation of the data?

Is there something I miss or is there any solution to this?
Thanks for any help!

cheers, jo



I tried this on different R-version (including 3.2.3 and 3.3.0 alpha); The
R-version I used for the code above is:
> sessionInfo()
R version 3.0.2 (2013-09-25)
Platform: x86_64-unknown-linux-gnu (64-bit)

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
 [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
 [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
 [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

FAQ 7.31

ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature and
Forest
team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance
Kliniekstraat 25
1070 Anderlecht
Belgium

To call in the statistician after the experiment is done may be no more
than asking him to perform a post-mortem examination: he may be able to say
what the experiment died of. ~ Sir Ronald Aylmer Fisher
The plural of anecdote is not data. ~ Roger Brinner
The combination of some data and an aching desire for an answer does not
ensure that a reasonable answer can be extracted from a given body of data.
~ John Tukey

2016-04-05 13:34 GMT+02:00 Rainer Johannes <Johannes.Rainer at eurac.edu>:
> Dear All,
>
> I have the following problem:
>
> I have a function in which I check if the difference between values is
> smaller or equal to a certain threshold. I however realized that I might
> get there some unexpected results:
>
> > abs(1 - 0.95) >= 0.05
> [1] TRUE
> ## So that?s fine, but:
> > abs(1 - 0.95) <= 0.05
> [1] FALSE
>
> Apparently, abs(1 - 0.95) is not equal to 0.05, which I find however quite
> disturbing.
>
> Along these lines:
> > abs(0.95 - 1) > 0.05
> [1] TRUE
> > abs(0.95 - 1) < 0.05
> [1] FALSE
>
> I guess that has to do with the floating point representation of the data?
>
> Is there something I miss or is there any solution to this?
> Thanks for any help!
>
> cheers, jo
>
>
>
> I tried this on different R-version (including 3.2.3 and 3.3.0 alpha); The
> R-version I used for the code above is:
>
> > sessionInfo()
> R version 3.0.2 (2013-09-25)
> Platform: x86_64-unknown-linux-gnu (64-bit)
>
> locale:
>  [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C
>  [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8
>  [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8
>  [7] LC_PAPER=en_US.UTF-8       LC_NAME=C
>  [9] LC_ADDRESS=C               LC_TELEPHONE=C
> [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
>
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
> ______________________________________________
> 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.
	[[alternative HTML version deleted]]

Yes, that does have to do with floating point representation.
I use this function for these types of comparisons (works with values as
well as with vectors):

check.equal <- function(x, y) {
    check.vector <- as.logical(unlist(lapply(x, all.equal, y)))
    check.vector[is.na(check.vector)] <- FALSE
    return(check.vector)
}

See:
?all.equal

Hth,
Adrian

On Tue, Apr 5, 2016 at 2:34 PM, Rainer Johannes <Johannes.Rainer at
eurac.edu>
wrote:
> Dear All,
>
> I have the following problem:
>
> I have a function in which I check if the difference between values is
> smaller or equal to a certain threshold. I however realized that I might
> get there some unexpected results:
>
> > abs(1 - 0.95) >= 0.05
> [1] TRUE
> ## So that?s fine, but:
> > abs(1 - 0.95) <= 0.05
> [1] FALSE
>
> Apparently, abs(1 - 0.95) is not equal to 0.05, which I find however quite
> disturbing.
>
> Along these lines:
> > abs(0.95 - 1) > 0.05
> [1] TRUE
> > abs(0.95 - 1) < 0.05
> [1] FALSE
>
> I guess that has to do with the floating point representation of the data?
>
> Is there something I miss or is there any solution to this?
> Thanks for any help!
>
> cheers, jo
>
>
>
> I tried this on different R-version (including 3.2.3 and 3.3.0 alpha); The
> R-version I used for the code above is:
>
> > sessionInfo()
> R version 3.0.2 (2013-09-25)
> Platform: x86_64-unknown-linux-gnu (64-bit)
>
> locale:
>  [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C
>  [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8
>  [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8
>  [7] LC_PAPER=en_US.UTF-8       LC_NAME=C
>  [9] LC_ADDRESS=C               LC_TELEPHONE=C
> [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
>
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
> ______________________________________________
> 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.



-- 
Adrian Dusa
University of Bucharest
Romanian Social Data Archive
Soseaua Panduri nr.90
050663 Bucharest sector 5
Romania

	[[alternative HTML version deleted]]

Thanks Adrian and Thierry (from the previous answer).

I was aware of the all.equal function, but there is nothing similar for <=
(e.g. all.smallerEqual)?

cheers, jo

On 05 Apr 2016, at 14:31, Adrian Du?a <dusa.adrian at
unibuc.ro<mailto:dusa.adrian at unibuc.ro>> wrote:

Yes, that does have to do with floating point representation.
I use this function for these types of comparisons (works with values as well as
with vectors):

check.equal <- function(x, y) {
    check.vector <- as.logical(unlist(lapply(x, all.equal, y)))
    check.vector[is.na<http://is.na/>(check.vector)] <- FALSE
    return(check.vector)
}

See:
?all.equal

Hth,
Adrian

On Tue, Apr 5, 2016 at 2:34 PM, Rainer Johannes <Johannes.Rainer at
eurac.edu<mailto:Johannes.Rainer at eurac.edu>> wrote:
Dear All,

I have the following problem:

I have a function in which I check if the difference between values is smaller
or equal to a certain threshold. I however realized that I might get there some
unexpected results:
> abs(1 - 0.95) >= 0.05
[1] TRUE
## So that?s fine, but:
> abs(1 - 0.95) <= 0.05
[1] FALSE

Apparently, abs(1 - 0.95) is not equal to 0.05, which I find however quite
disturbing.

Along these lines:
> abs(0.95 - 1) > 0.05
[1] TRUE
> abs(0.95 - 1) < 0.05
[1] FALSE

I guess that has to do with the floating point representation of the data?

Is there something I miss or is there any solution to this?
Thanks for any help!

cheers, jo



I tried this on different R-version (including 3.2.3 and 3.3.0 alpha); The
R-version I used for the code above is:
> sessionInfo()
R version 3.0.2 (2013-09-25)
Platform: x86_64-unknown-linux-gnu (64-bit)

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C
 [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8
 [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8
 [7] LC_PAPER=en_US.UTF-8       LC_NAME=C
 [9] LC_ADDRESS=C               LC_TELEPHONE=C
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base
______________________________________________
R-help at r-project.org<mailto: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<http://www.r-project.org/posting-guide.html>
and provide commented, minimal, self-contained, reproducible code.



--
Adrian Dusa
University of Bucharest
Romanian Social Data Archive
Soseaua Panduri nr.90
050663 Bucharest sector 5
Romania


	[[alternative HTML version deleted]]

> Apparently, abs(1 - 0.95) is not equal to 0.05, which I find however quite
> disturbing.
It's normal.* See R FAQ 7.31 in the html help system.

S Ellison

*... and common to all computers that use binary. 



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Hi
> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of S
Ellison
> Sent: Wednesday, April 6, 2016 12:35 PM
> To: Rainer Johannes <Johannes.Rainer at eurac.edu>; r-help at
r-project.org
> Subject: Re: [R] Problem with <= (less than or equal): not giving the
expected
> result
>
> > Apparently, abs(1 - 0.95) is not equal to 0.05, which I find however
> > quite disturbing.
>
> It's normal.* See R FAQ 7.31 in the html help system.
>
> S Ellison
>
> *... and common to all computers that use binary.
The main issue is that when using Excel you do not experience normally such
issues, probably because Excel silently decide how to express precision of
decimal values.

=+ABS(1-0.995) is equal to 0.005, however
=+ABS(1-0.9995) is not equal to 0.0005

So it when Excel (Excel 2016) users do not use numbers smaller than 0.005 they
do not find this behaviour.

Cheers
Petr


>
>
>
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> message and any copies from your computer and network.
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> Registered office: Queens Road, Teddington, Middlesex, TW11 0LY, UK
> ______________________________________________
> 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.
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