Marc You have been given the answer already and a solution. See the R FAQ 7.31. As you have discovered this issue is not specific to R. In order to eliminate this "problem" entirely, you will need a computer system with infinite precision.
Dan Daniel J. Nordlund Washington State Department of Social and Health Services Planning, Performance, and Accountability Research and Data Analysis Division Olympia, WA 98504-5204 > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-bounces@r- > project.org] On Behalf Of Marc Jekel > Sent: Monday, January 24, 2011 11:48 AM > Cc: r-help@r-project.org > Subject: Re: [R] sensitivity logical operators in R > > Hi again, > > I have checked the same code (see below) using MATLAB. It produces the > same error (i.e., equal numbers are evaluated as unequal). Do I miss > something? > > Thanks for help! > > Marc > > Marc Jekel schrieb: > > Hello R Fans, > > > > Another question for the community that really frightened me today. > > The following logical comparison produces a "false" as output: > > > > t = sum((c(.7,.69,.68,.67,.66)-.5)*c(1,1,-1,-1,1)) > > tt = sum((c(.7,.69,.68,.67,.66)-.5)*c(1,-1,1,1,-1)) > > > > t == tt > > > > This is really strange behavior. Most likely this has something to do > > how R represents numbers internally and the possible sensitivity of a > > computer? Does anyone know when this strange behavior occurs and how > > to fix it? > > > > Thank you all! This list is pleasure!!! > > > > Marc > > > > ______________________________________________ > 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. ______________________________________________ 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.
