Depending on how you are using POSIXct, you accuracy is limited to the microsecond level. It is stored as a floating point number with 54 bit of accuracy (~16 digits) and currently the number of seconds since 1/1/1970 is 10 digits, so with microseconds adding 6 more, you are at the limit:
> x <- Sys.time() > x [1] "2010-02-06 09:34:58 EST" > unclass(x) [1] 1265466899 > x [1] "2010-02-06 09:34:58 EST" > y <- x+.000001 > x-y Time difference of -9.536743e-07 secs > y <- x+.0000001 > x-y Time difference of 0 secs > y <- x+.000001 # 1 us > identical(x,y) [1] FALSE > y <- x+.0000001 # 0.1 us > identical(x,y) [1] TRUE > On Sat, Feb 6, 2010 at 9:41 AM, Laurent Rhelp <laurentrh...@free.fr> wrote: > Gabor Grothendieck a écrit : > >> zoo is independent of time and date class so it does not restrict your >> choice of index class. POSIXct supports sub-microsecond accuracy. >> See ?POSIXct . Simply using the number of microseconds since the >> start of the experiment is another possibility. >> >> On Sat, Feb 6, 2010 at 8:25 AM, Laurent Rhelp <laurentrh...@free.fr> >> wrote: >> >>> >>> Dear R-List, >>> >>> I have the habit of using R for my data processing and I like to use the >>> power of the lattice package. Presently, I have to manage time series. >>> So, >>> in order to work properly I want to discover the zoo package and the >>> related >>> methods (since lattice can work with zoo class). But my physical >>> experiment >>> lasts only one second and my sampling period is equal to 1 microsecond >>> (the >>> date time value is given by the IRIG Card for my data acquisition card). >>> I >>> read the R-News june 2004 about the date time Classes in R and there is >>> no >>> information about allowing for the microseconds. So do you think it is >>> really a good idea to try to use the R time series framework (zoo package >>> for example) with my data ? Or would there be a tip ? >>> >>> Thank you very much >>> >>> Laurent >>> >>> ______________________________________________ >>> 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. >>> >>> >> >> > > Thank you, I will see in details the POSIXct class. > > ______________________________________________ > 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. > -- Jim Holtman Cincinnati, OH +1 513 646 9390 What is the problem that you are trying to solve? ______________________________________________ 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.
