jan.hattendorf at unibas.ch
2009-Aug-01 20:05 UTC
[Rd] incorrect result (41/10-1/10)%%1 (PR#13863)
Full_Name: jan hattendorf
Version: 2.9.0
OS: XP
Submission from: (NULL) (213.3.108.185)
I get an incorrect result for
(41/10-1/10)%%1
[1] 1
The error did not occur with other numbers than 41 (1, 11, 21, 31, 51, ...)
test <- rep(NA, 1000)
for(i in 1:1000){
test[i] <- i/10-1/10
}
test[test%%1==0]
jan.hattendorf at unibas.ch wrote:> Full_Name: jan hattendorf > Version: 2.9.0 > OS: XP > Submission from: (NULL) (213.3.108.185) > > > I get an incorrect result for > > (41/10-1/10)%%1 > > [1] 1 > > The error did not occur with other numbers than 41 (1, 11, 21, 31, 51, ...) > > > test <- rep(NA, 1000) > for(i in 1:1000){ > test[i] <- i/10-1/10 > } > test[test%%1==0] > > ______________________________________________ > R-devel at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-develFAQ 7.31 -- O__ ---- Peter Dalgaard ?ster Farimagsgade 5, Entr.B c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk) FAX: (+45) 35327907
Good morning Jan, Could this be covered off by the following? http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these-numbers-are-equal_003f Kind regards, Sean On Sat, Aug 1, 2009 at 9:05 PM, <jan.hattendorf at unibas.ch> wrote:> Full_Name: jan hattendorf > Version: 2.9.0 > OS: XP > Submission from: (NULL) (213.3.108.185) > > > I get an incorrect result for > > (41/10-1/10)%%1 > > [1] 1 > > The error did not occur with other numbers than 41 (1, 11, 21, 31, 51, ...) > > > test <- rep(NA, 1000) > for(i in 1:1000){ > ?test[i] <- i/10-1/10 > } > test[test%%1==0] > > ______________________________________________ > R-devel at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel >
Not a bug, just a FAQ (7.31). http://CRAN.R-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these-numbers-are-equal_003f On Sat, 1 Aug 2009, jan.hattendorf at unibas.ch wrote:> Full_Name: jan hattendorf > Version: 2.9.0 > OS: XP > Submission from: (NULL) (213.3.108.185) > > > I get an incorrect result for > > (41/10-1/10)%%1 > > [1] 1 > > The error did not occur with other numbers than 41 (1, 11, 21, 31, 51, ...) > > > test <- rep(NA, 1000) > for(i in 1:1000){ > test[i] <- i/10-1/10 > } > test[test%%1==0] > > ______________________________________________ > R-devel at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel > >
This is not a bug. It is a case of R FAQ 7.34:
http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-the
se-numbers-are-equal_003f
------------------------------------------------------------------------
----
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature
and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium
tel. + 32 54/436 185
Thierry.Onkelinx at inbo.be
www.inbo.be
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
-----Oorspronkelijk bericht-----
Van: r-devel-bounces at r-project.org
[mailto:r-devel-bounces at r-project.org] Namens jan.hattendorf at unibas.ch
Verzonden: zaterdag 1 augustus 2009 22:05
Aan: r-devel at stat.math.ethz.ch
CC: R-bugs at r-project.org
Onderwerp: [Rd] incorrect result (41/10-1/10)%%1 (PR#13863)
Full_Name: jan hattendorf
Version: 2.9.0
OS: XP
Submission from: (NULL) (213.3.108.185)
I get an incorrect result for
(41/10-1/10)%%1
[1] 1
The error did not occur with other numbers than 41 (1, 11, 21, 31, 51,
...)
test <- rep(NA, 1000)
for(i in 1:1000){
test[i] <- i/10-1/10
}
test[test%%1==0]
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> I get an incorrect result for > > (41/10-1/10)%%1 > > [1] 1Note that due to rounding errors, 41/10-1/10 is formatC(41/10-1/10, digits=20) # [1] "3.9999999999999995559" Besides FAQ 7.31, related information may be found also at http://wiki.r-project.org/rwiki/doku.php?id=misc:r_accuracy Petr.