On Fri, May 22, 2009 at 1:55 PM, Stavros Macrakis <macra...@alum.mit.edu> wrote: > On Fri, May 22, 2009 at 12:28 PM, Gabor Grothendieck > <ggrothendi...@gmail.com> wrote: > >> ...The way this might appear in code is if someone wanted to calculate the >> number of one hour intervals in 18 hours. One could write: >> >> t18 <- times("18:00:00") >> t1 <- times("1:00:00") >> as.numeric(t18) / as.numeric(t1) >> >> but since we all know that it uses internal representations unless it >> indicates otherwise > > Um, yes, I suppose that was the attitude in the 60's and 70's, but I think > we have moved on from there. cf. > http://en.wikipedia.org/wiki/Data_abstraction > >> >> a typical code snippet might shorten it to: >> >> as.numeric(t18 / t1) >> >> and all such code would break if one were to cause that to generate an >> error. > > (18/24 day)/(1/24 day) is the perfectly meaningful dimensionless number 18, > so this code should not break with a correct implementation of '/'. (cf. > http://en.wikipedia.org/wiki/Dimensional_analysis). Alas, chron gives the > nonsense result of 18 days.
Your point was that otherwise undefined operations should produce an error and I was illustrating why that could not be introduced at this stage. I had already suggested that you implement division if you found it important and that was not the source of any disagreement. ______________________________________________ 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.