[R] numeric not equal its value
Dear R users, I ran into the strange situation where a number does not seem to equal its value. Try this: a - seq(0.05,0.7,0.05)[3] b - 0.15 a == b Should this not be TRUE? a-b yields a very small number (and not 0) so this most probably is a numerical error, but why does seq create such numbers? Thanks a lot Jannis __ 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.
Re: [R] numeric not equal its value
Hi. Check R FAQ, section 7.31 Why doesn't R think these numbers are equal? http://cran.r-project.org/doc/FAQ/R-FAQ.html all.equal(a,b) Andrija On Mon, May 20, 2013 at 2:36 PM, Jannis bt_jan...@yahoo.de wrote: Dear R users, I ran into the strange situation where a number does not seem to equal its value. Try this: a - seq(0.05,0.7,0.05)[3] b - 0.15 a == b Should this not be TRUE? a-b yields a very small number (and not 0) so this most probably is a numerical error, but why does seq create such numbers? Thanks a lot Jannis __** R-help@r-project.org mailing list https://stat.ethz.ch/mailman/**listinfo/r-helphttps://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/** posting-guide.html http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. [[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.
Re: [R] numeric not equal its value
Hello, That's FAQ 7.31. Note that the increment, 0.05, is not a power of 2 so the third value of the sequence is not exactly equal to 0.15. Hope this helps, Rui Barradas Em 20-05-2013 13:36, Jannis escreveu: Dear R users, I ran into the strange situation where a number does not seem to equal its value. Try this: a - seq(0.05,0.7,0.05)[3] b - 0.15 a == b Should this not be TRUE? a-b yields a very small number (and not 0) so this most probably is a numerical error, but why does seq create such numbers? Thanks a lot Jannis __ 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.
Re: [R] numeric not equal its value
Jannis, Not strange. Try with numbers that can be exactly represented in binary (that's what computers use), e.g., a-seq(5,70,by=5) b-15 a==b or fractions, a-seq(1/32,14/32,by=1/32) b-3/32 a==b Most decimal fractions cannot be represented exactly although a bit of magic will display them as if they are. A little digging into the r-help archives will find further explanation. Clint Clint BowmanINTERNET: cl...@ecy.wa.gov Air Quality Modeler INTERNET: cl...@math.utah.edu Department of Ecology VOICE: (360) 407-6815 PO Box 47600FAX:(360) 407-7534 Olympia, WA 98504-7600 USPS: PO Box 47600, Olympia, WA 98504-7600 Parcels:300 Desmond Drive, Lacey, WA 98503-1274 On Mon, 20 May 2013, Jannis wrote: Dear R users, I ran into the strange situation where a number does not seem to equal its value. Try this: a - seq(0.05,0.7,0.05)[3] b - 0.15 a == b Should this not be TRUE? a-b yields a very small number (and not 0) so this most probably is a numerical error, but why does seq create such numbers? Thanks a lot Jannis __ 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.
