That is not strange behaviour. It's a case of FAQ 7.31: http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these-numbers-are-equal_003f
HTH, Thierry ---------------------------------------------------------------------------- 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.onkel...@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-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] Namens Žroutík Verzonden: donderdag 12 februari 2009 16:20 Aan: r-help@r-project.org Onderwerp: [R] trunc/floor a number -- strange bahaviour Hi everybody, given a fresh rgui.exe load on winxp OS, I enter (a minimal exaple) n <- 12.357531 Then the following command: n <- (n - floor(n))*10; n gives the following outputs: [1] 3.57531 [1] 5.7531 [1] 7.531 [1] 5.31 [1] 3.1 [1] 1 === still as expected [1] 10 === not expected, count with me: 1 - floor(1) is zero, times 10 gives 0, not 10!!!! [1] 10 === should stay forever zero (0) [1] 10 [1] 9.999998 [1] 9.999982 [1] 9.999821 [1] 9.998212 The sama happens with trunc(). e.g. (a minimal exaple) n <- 0.245 n <- (n - trunc(n))*10; n [1] 2.45 [1] 4.5 [1] 5 [1] 1.776357e-13 ===== zero expected!!! [1] 1.776357e-12 And I'm asking "what the heck?!" and where is the bug in my examples? Any suggestion well appreciated. p.s. The expression with floor() and trunc() are to be implemented in a function which gives a value equal precision order of the given number. e.g. 12.345 would have (-3), 12.1 would have (-1), 12 would have (0) and e.g. 12000 would have the order of the precision (4). Basically, it is the order of the last given non-zero digit. [[alternative HTML version deleted]] ______________________________________________ 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. Dit bericht en eventuele bijlagen geven enkel de visie van de schrijver weer en binden het INBO onder geen enkel beding, zolang dit bericht niet bevestigd is door een geldig ondertekend document. The views expressed in this message and any annex are purely those of the writer and may not be regarded as stating an official position of INBO, as long as the message is not confirmed by a duly signed document. ______________________________________________ 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.
