Plus, current dates are an awful lot of seconds since 1970-01-01, so the relative error on second-scale differences is bigger than you might think:
> as.numeric(Sys.time()) [1] 1441874878 and since relative representation errors are of the order 1e-16, the corresponding absolute errors are about 1e-7. (The examples given forgot to tell us what nom_fich is supposed to be, but I assume something relatively current was meant.) -pd On 09 Sep 2015, at 16:50 , Sarah Goslee <sarah.gos...@gmail.com> wrote: > Looks like R FAQ 7.31 to me. > > https://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these-numbers-are-equal_003f > > On Wed, Sep 9, 2015 at 4:19 AM, DE <david.ecoti...@cerema.fr> wrote: >> Hi, >> >> I'd like to create a date-time seq with a period of 0.05 s, over several >> days. >> >> # try : >> start<-strptime(nom_fich,format="%y%m%d") >> time<-seq(from=start, by=0.05, length.out = 86400*20*3) >> print(as.POSIXlt(time[2])$sec) >> # result is 0.04999995 and not 0.05 as expected >> >> But If I am looking at the sequence, the seconds are not separated by 0.05, >> but by something very close (0.04999995). Same pb if I want to add a >> fraction of seconds to a date-time object : >> >> # try : >> start<-strptime(nom_fich,format="%y%m%d") >> as.POSIXlt(start+0.05,origin="1970-01-01")$sec >> # result is 0.04999995 and not 0.05 as expected >> >> Any idea to solve this pb ? >> >> Thank you in advance ! >> >> > > > -- > Sarah Goslee > http://www.functionaldiversity.org > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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. -- Peter Dalgaard, Professor, Center for Statistics, Copenhagen Business School Solbjerg Plads 3, 2000 Frederiksberg, Denmark Phone: (+45)38153501 Office: A 4.23 Email: pd....@cbs.dk Priv: pda...@gmail.com ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.
