[R] Unknown anomaly

Bert Gunter bgunter.4567 at gmail.com
Wed Apr 19 05:12:58 CEST 2017

```FAQ 7.31.

-- Bert

(The FAQ's exist for a reason. You should read them!)

Bert Gunter

"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )

On Tue, Apr 18, 2017 at 7:53 PM, Boris Steipe <boris.steipe at utoronto.ca> wrote:
> The concept of equality for numbers that are represented on a computer is frequently misapplied. Consider:
>
> a <- seq(from=0, to=1, by=0.02)
>
> print(a[36])
> [1] 0.7
>
> a[36] == 0.7
> [1] FALSE
>
> print(a[36], digits=22)
> [1] 0.7000000000000000666134
>
> a[36] == 0.7000000000000001
> [1] TRUE
>
> All clear?
>
>
> B.
>
>
>
>> On Apr 18, 2017, at 9:55 PM, Benjamin Robira <robira at clipper.ens.fr> wrote:
>>
>> Dear Sir,
>>
>> I writting to you as I am facing an irregularity in R that I do not know
>> the origin. When doing a sequence from 0 to 1 by 0.02 and assigning it to
>> a vector (i.e. code: a <- seq(from=0, to=1, by=0.02)) then, when I try to
>> use the 36th element (and two others behave the same way) it is not
>> recognized correctly. For instance a[36]==0.7, what should give TRUE,
>> gives instead FALSE. However, this works fine for element 35 and 37 and
>> all other elements but two.
>> I do not know the reason. I restarted my R session and tried on another
>> computer. This has been the same. None of my colleagues had an answer. I
>> hope that you would be able to help me fix that as it must be a pretty
>> straightforward error that I do not realise.
>>
>> I would be thankful for any help,
>> With my very Best Regards,
>> Benjamin.
>>
>> ______________________________________________
>> 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.

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