Well...thanks to everybody for suggestions and reading...I guess I have to study more!
Enrico On 28 Oct 2010, at 11:48, Rainer M Krug wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > On 28/10/10 12:23, Enrico R. Crema wrote: >> Dear List, >> >> I've been running a numerical simulation and I found this odd error in my >> code where the which command could not identify which rows of a column of >> data.frame were corresponding to the value 0.3. There are 7 unique values in >> this column (0.01,0.05,0.1,0.2,0.3,0.4,0.5), and this does not work only for >> 0.3. So I looked at the column and manually tried to use the which() >> command, and the results were all FALSE despite I could see those number. So >> I recreated my sequence of number and tested: >> >> seq(0.1,0.5,0.1)[3]==0.3 >> >> which gave me FALSE!!! All the other numbers (0.1,0.2,0.4,0.5) give me TRUE, >> but 0.3 was not working. So I did: >> >> seq(0.1,0.5,0.1)[3]-0.3 >> >> which gave me 5.551115e-17. If you run a similar sequence like: >> >> seq(0.2,0.6,0.1)[2]==0.3 >> >> this will still give me FALSE. No, for my own purpose, I fixed the problem >> in this way: >> >> zerothree=seq(0.1,0.5,0.1)[3] >> which(data[,1]==zerothree) >> >> but I guess this bug is a bit of problem...Apologies if it is the wrong >> place to post this bug, and apologies also if this was a known issue. My >> version of R is : >> >> platform x86_64-pc-linux-gnu >> arch x86_64 >> os linux-gnu >> system x86_64, linux-gnu >> status >> major 2 >> minor 10.1 >> year 2009 >> month 12 >> day 14 >> svn rev 50720 >> language R >> version.string R version 2.10.1 (2009-12-14) > > This is not a bug, but based on the internal representation of numbers > in the binary format. Numbers like 0.3 can not be represented as exactly > 0.3, wherefore errors accumulate in a sequence. > > I can't provide you a link for more details, but the topic comes up > every now and then in this mailing list. > > Cheers, > > Rainer > >> >> >> Many Thanks, >> >> Enrico >> >> ______________________________________________ >> R-help@r-project.org mailing list >> 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. > > > - -- > Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation > Biology, UCT), Dipl. Phys. (Germany) > > Centre of Excellence for Invasion Biology > Natural Sciences Building > Office Suite 2039 > Stellenbosch University > Main Campus, Merriman Avenue > Stellenbosch > South Africa > > Tel: +33 - (0)9 53 10 27 44 > Cell: +27 - (0)8 39 47 90 42 > Fax (SA): +27 - (0)8 65 16 27 82 > Fax (D) : +49 - (0)3 21 21 25 22 44 > Fax (FR): +33 - (0)9 58 10 27 44 > email: rai...@krugs.de > > Skype: RMkrug > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1.4.10 (GNU/Linux) > Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ > > iEYEARECAAYFAkzJVOEACgkQoYgNqgF2egpVXACeNO9GyRh9XKLg1g4EhcFs4Qa5 > WXgAmgOdNB/xgmRS4UsMaEtunxS6NB/u > =azme > -----END PGP SIGNATURE----- ______________________________________________ R-help@r-project.org mailing list 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.