To answer part 1) of your question, see point 7.31 in the R FAQ (http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these- numbers-are-equal_003f).
> 0.3 - 3*0.1 [1] -5.551115e-17 It always amazes me in how many different guises the problem of floating point representation crops up. HTH >-----Original Message----- >From: [EMAIL PROTECTED] >[mailto:[EMAIL PROTECTED] On Behalf Of >Jonathan Williams >Sent: 22 November 2006 12:15 PM >To: Ethz. Ch >Subject: [R] odd behaviour of %%? > >Dear R Helpers, > >I am trying to extract the modulus from divisions by a >sequence of fractions. >I noticed that %% seems to behave inconsistently (to my untutored eye), >thus: > >> 0.1%%0.1 >[1] 0 >> 0.2%%0.1 >[1] 0 >> 0.3%%0.1 >[1] 0.1 >> 0.4%%0.1 >[1] 0 >> 0.5%%0.1 >[1] 0.1 >> 0.6%%0.1 >[1] 0.1 >> 0.7%%0.1 >[1] 0.1 >> 0.8%%0.1 >[1] 0 >> 0.9%%0.1 > >The modulus for 0.1, 0.2, 0.4 and 0.8 is zero, as I'd expect. >But, the modulus for 0.3, 0.6, 0.7 and 0.9 is 0.1 - which I >did not expect. I can see no obvious rule that predicts >whether x%%0.1 will give an answer of 0 or 0.1. I could find >no explanation of the way that %% works in the R manuals. So, I have 3 >questions:- > >1) Why is the modulus of 0.3%%0.1 (and 0.5%%0.1 and >0.6%%0.1...) not zero? >2) Are there any algorithms in R that use the %% operator with >fractional divisors in this way, and do they know about its >apparently inconsistent behaviour? >3) If %% is not intended for use with fractional divisors, >then would it be a good idea to trap attempts to use them? > >Thanks, in advance, for your help > >Jonathan Williams > >______________________________________________ >R-help@stat.math.ethz.ch 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. > ******************** Nedbank Limited Reg No 1951/000009/06. The following link displays the names of the Nedbank Board of Directors and Company Secretary. [ http://www.nedbank.co.za/terms/DirectorsNedbank.htm ] This email is confidential and is intended for the addressee only. The following link will take you to Nedbank's legal notice. [ http://www.nedbank.co.za/terms/EmailDisclaimer.htm ] ******************** [[alternative HTML version deleted]] ______________________________________________ R-help@stat.math.ethz.ch 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.
