----- Original Message ----- From: "Gavin Simpson" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Cc: <r-devel@stat.math.ethz.ch> Sent: Friday, July 07, 2006 1:15 PM Subject: Re: [Rd] BUG in " == " ? (PR#9065)
> On Fri, 2006-07-07 at 11:50 +0200, [EMAIL PROTECTED] wrote: >> Hello, >> here is the version of R that I use : >> >> > version >> _ >> platform i486-pc-linux-gnu >> arch i486 >> os linux-gnu >> system i486, linux-gnu >> status >> major 2 >> minor 3.1 >> year 2006 >> month 06 >> day 01 >> svn rev 38247 >> language R >> version.string Version 2.3.1 (2006-06-01) >> >> And here is one of the sequences of isntruction that returns an >> abberation : >> >> > x<-seq(0,1,by=0.01) >> > x[71] >> [1] 0.7 >> > which(x == 0.7) >> numeric(0) >> > x[71] == 0.7 >> [1] FALSE >> >> Or another version of (maybe) the same bug : >> >> > x <- 70 >> > x == 70 >> [1] TRUE >> > x <- x*0 >> > x <- 70 >> > x == 70 >> [1] TRUE >> > x<-x*0.01 >> > x >> [1] 0.7 >> > x == 0.7 >> [1] FALSE >> >> It seems completely strange ... any help would be greatly >> appreciated :) >> >> Regards, >> Eric Durand > > Not a bug. Floating point precision - see > http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these-numbers-are-equal_003f > > E.g.: > > x <- seq(0,1,by=0.01) > x[71] > which(x == 0.7) # FALSE > all.equal(0.7, x[71]) # TRUE > > all.equal() should be used for this type of comparison. See > ?all.equal > > You could achieve what you wanted by something like this [ if you > have a > real need to use which() ]: > > x <- c(0.7, x, 0.7) # more 0.7's > lims <- range(0.7 + .Machine$double.eps^0.5, 0.7 - > .Machine$double.eps^0.5) > which(x >= lims[1] & x <= lims[2]) > > Not sure if this is a good way to do it or not? > > If you need to do this kind of comparison with which(), having a > v.all.equal() do a vectorised version of all.equal() would be > useful, > returning a vector of TRUE/FALSE for each comparison. Maybe this > already > exists somewhere? > > E.g.: > > v.all.equal <- function(x, y) { > apply(as.matrix(x), 1, function(x, y) { > retval <- as.logical(all.equal(x, y)) > retval[is.na(retval)] <- FALSE > retval > }, y) > } > > which(v.all.equal(x, 0.7)) # 1 72 103 in this case I think it's simpler to do something like: which(as.logical(sapply(x, all.equal, target = 0.7))) Best, Dimitris ---- Dimitris Rizopoulos Ph.D. Student Biostatistical Centre School of Public Health Catholic University of Leuven Address: Kapucijnenvoer 35, Leuven, Belgium Tel: +32/(0)16/336899 Fax: +32/(0)16/337015 Web: http://med.kuleuven.be/biostat/ http://www.student.kuleuven.be/~m0390867/dimitris.htm > Again, maybe this is a bad thing...? In which case, I guess I'm > about to > get told so... ;-) > > G > -- > %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% > Gavin Simpson [t] +44 (0)20 7679 0522 > ECRC & ENSIS, UCL Geography, [f] +44 (0)20 7679 0565 > Pearson Building, [e] gavin.simpsonATNOSPAMucl.ac.uk > Gower Street, London [w] http://www.ucl.ac.uk/~ucfagls/cv/ > London, UK. WC1E 6BT. [w] http://www.ucl.ac.uk/~ucfagls/ > %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% > > ______________________________________________ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel > Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
