Yes! Chuck's use of mapply is exactly the split/combine strategy I was looking for. In retrospect, exactly how one should think about it. Many thanks to all for a constructive discussion .
-- Bert Bert Gunter "Data is not information. Information is not knowledge. And knowledge is certainly not wisdom." -- Clifford Stoll On Wed, Sep 16, 2015 at 12:40 AM, peter dalgaard <pda...@gmail.com> wrote: > I think a more common idiom for the simpler case would be to use indexing > > vals <- c(0.1, 0.15, 0.2) > mult <- vals[ASBclass] > > (However, some people are on the move to enforce > > mult <- vals[as.numeric(ASBclass)] > > because people who confuse factors and character variables get even more > confused about factor indexing being different from character indexing.) > > For the more complex cases, I think Chuck's split/unsplit principle is the > ticket. For one thing, you avoid silliness like (X >= 0) * sqrt(X) + (X < 0) > * -sqrt(-X) coming out with warnings from calculating the non-selected > alternative. > > -pd > >> On 16 Sep 2015, at 07:56 , Anthoni, Peter (IMK) <peter.anth...@kit.edu> >> wrote: >> >> Hi, >> >> I guess this might work too and might be quite speedy: >> >> ASBclass = factor(c(1,2,2,3,2,1)) >> Flow = c(1,1,1,1,1,1) >> >> mult = ((ASBclass==1) * 0.1 + (ASBclass==2) * 0.15 + (ASBclass==3) * 0.2) >> deviation = mult * Flow >> >> or with the more complex arithmetic: >> >> deviation = ((ASBclass==1) * (Flow*2) + (ASBclass==2) * (Flow+3) + >> (ASBclass==3) * sqrt(Flow)) >> >> cheers >> Peter >> >> >> >>> On 16 Sep 2015, at 04:20, Charles C. Berry <ccbe...@ucsd.edu> wrote: >>> >>> On Tue, 15 Sep 2015, Bert Gunter wrote: >>> >>>> Thanks to both Davids. >>>> >>>> I realize that these things are often a matter of aesthetics -- and >>>> hence have little rational justification -- but I agree with The Other >>>> David: eval(parse) seems to me to violate R's soul( it makes R a macro >>>> language instead of a functional one). >>>> >>>> However, mapply(... switch) effectively loops through the frame row by >>>> row. Aesthetically, I like it; but it seems inefficient. If there are >>>> e.g. 1e6 rows in say 10 categories, I think Jeff's approach should do >>>> much better. I'll try to generate some actual data to see unless >>>> someone else beats me to it. >>> >>> Use mapply like this on large problems: >>> >>> unsplit( >>> mapply( >>> function(x,z) eval( x, list( y=z )), >>> expression( A=y*2, B=y+3, C=sqrt(y) ), >>> split( dat$Flow, dat$ASB ), >>> SIMPLIFY=FALSE), >>> dat$ASB) >>> >>> Chuck >>> >>> ______________________________________________ >>> 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. >> >> ______________________________________________ >> 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 > 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. ______________________________________________ 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.
