You didn't mention it, but did you use something like options(digits=20) before displaying that data? In any case, > 1000000000000.4000244 == 1000000000000.4 [1] TRUE because R uses the IEEE-754 double precision floating point arithmetic that all modern computers support. That gives you 52 binary digits of precision, somewhat less than 17 decimal digits, so your difference in the 18th digit is ignored.
If you need more than 16 decimal digits of precision, you could break the numbers into parts (via string manipulation, before reading them as numbers) and or use a high precision package like Rmpfr to manipulate them (it will be slow and has limited functionality). Bill Dunlap Spotfire, TIBCO Software wdunlap tibco.com > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On > Behalf > Of Istvan Nemeth > Sent: Friday, May 04, 2012 6:55 AM > To: r-help@r-project.org > Subject: [R] read-in, error??? > > Dear Users! > > I encountered with some problem in data reading while I challenged R (and > me too) in a validation point of view. > In this issue, I tried to utilize some reference datasets ( > http://www.itl.nist.gov/div898/strd/index.html). > And the result departed a bit from my expectations. This dataset dedicated > to challenge cancellation and accumulation errors (case SmLs07), that's why > this uncommon look of txt file. > > Treatment Response > 1 1000000000000.4 > 1 1000000000000.3 > 1 1000000000000.5 > ...... > 2 1000000000000.2 > 2 1000000000000.4 > ..... > 3 1000000000000.4 > 3 1000000000000.6 > 3 1000000000000.4 > ......... > then after a read.table() I expect the same set instead I've got this: > > Treatment Response > 1 1 1000000000000.4000244 > 2 1 1000000000000.3000488 > 3 1 1000000000000.5000000 > ......... > 22 2 1000000000000.3000488 > 23 2 1000000000000.1999512 > 24 2 1000000000000.4000244 > ....... > 58 3 1000000000000.4000244 > 59 3 1000000000000.5999756 > 60 3 1000000000000.4000244 > 61 3 1000000000000.5999756 > 62 3 1000000000000.4000244 > ...... > a lots of number from the space. I assume that these numbers come from the > binary representation of such a tricky decimal numbers but my question is > how can I avoid this feature of the binary representation? > > Moreover, I wondered that it may raise some question in a regulated > environment. > > [[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. ______________________________________________ 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.
