Hi Markus, The R function round() uses the round-to-even method, which is explained on http://en.wikipedia.org/wiki/Rounding#Round-to-even_method.
If you would like instead "traditional rounding" then you should add 0.5 and take the integer part, as is suggested in the examples on ?round, e.g. x=c(1.49,1.50,1.51,2.49,2.50,2.51,3.49,3.50,3.51);r2e=round(x);trad=floor(x+0.5);data.frame(x,r2e,trad) The reason for the IEEE standard is to do with signal processing and the bias introduced by traditional rounding if you have a lot of data points whose decimal expansion ends in ....5. Personally, I am a mathematician and satistician and I find that in 99% of cases traditional rounding is what is required (basically always except some very specific examples involving very large sets of data) so for R to have put the IEEE standard as the default (rather than, say, an option) is a bit odd. However, R's benefits and advantages by far outweigh its little oddities, as I presume you know since you are using it. Effectively, I never use the round() command and always calculate using the floor function. Toby Marthews Le Dim 15 juin 2008 11:26, Markus Didion a écrit : > Dear R-users > > with a bit of grief I had to repeat an extensive analysis because I > did not suspect (and therefore did not read the documentation) that > round was implemented as "for rounding off a 5, the IEC 60559 standard > is expected to be used, 'go to the even digit'", resulting in > round(1.5) = 2 > round (2.5) = 2. > > As a non-mathematician I am both puzzled and intrigued by this rule as > it is against what I have learned in my math courses, i.e. > round(1.5) = 2 > round (2.5) = 3. > > I would like to understand the reason behind this rule. > > Thanks for your comments. > > Markus > > -- > > Markus Didion > > Wald?kologie Forest Ecology > Inst. f. Terrestrische Oekosysteme Inst. of Terrestrial Ecosystems > Departement Umweltwissenschaften Dept. of Environmental Sciences > Eidg. Technische Hochschule Swiss Fed. Inst. of Technology > ETH-Zentrum CHN G78 ETH-Zentrum CHN G78 > Universit?tstr. 22 > Universitaetstr. 22 > CH-8092 Z?rich CH-8092 Zurich > Schweiz > Switzerland > > Tel +41 (0)44 632 5629 Fax +41 (0)44 632 1358 > Email [EMAIL PROTECTED] > homepage: http://www.fe.ethz.ch/people/didionm ______________________________________________ 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.
