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.
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.
This is the standard behavior of floating point arithmetic on a
digital computer. Computers use 53-bit finite precision arithmetic.
They do not use infinite precision real numbers. Please see FAQ 7.31
for details.
The FAQ is in the R documentation on your computer in file
system.file("../../doc/FAQ")
Locate the file from the R prompt and then open in your favorite text editor.
On Tue, 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.
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.
On 19/04/17 13:55, Benjamin Robira 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.See FAQ 7.31. cheers, Rolf Turner -- Technical Editor ANZJS Department of Statistics University of Auckland Phone: +64-9-373-7599 ext. 88276