Dear Arun, Thanks for your suggestion, that does the trick. Just because I'm curious, where does the problem come from? I figured that wrapping the formula object in brackets would work as well:
aggregate((mF), d, mean) So I guess it has something to do with the scope of mF, or what is the root cause? Thanks for your help! KR, -Thorn > -----Original Message----- > From: arun [mailto:smartpink...@yahoo.com] > Sent: Mittwoch, 31. Oktober 2012 13:15 > To: Thaler,Thorn,LAUSANNE,Applied Mathematics > Cc: R help > Subject: Re: [R] aggregate.formula: formula from string > > Hi, > Try this: > res<- aggregate(eval(mF),d,mean) > > res > > # a b NA NA > #1 1 A -1.48354978 -0.37141485 > #2 2 A -0.08862713 0.35359250 > #3 3 A 1.17519518 -0.47595290 > #4 1 B 0.10214686 -0.70005131 > #5 2 B 0.41185154 0.03707291 > #6 3 B 0.20507062 -0.67946389 > > > res1<-aggregate(cbind(y, z) ~ a + b, d, mean) > colnames(res)[3:4]<-colnames(res1)[3:4] > identical(res,res1) > #[1] TRUE > A.K. > > > > > ----- Original Message ----- > From: "Thaler,Thorn,LAUSANNE,Applied Mathematics" > <thorn.tha...@rdls.nestle.com> > To: "r-help@r-project.org" <r-help@r-project.org> > Cc: > Sent: Wednesday, October 31, 2012 5:46 AM > Subject: [R] aggregate.formula: formula from string > > Dear all, > > I want to use aggregate.formula to conveniently summarize a data.frame. I have > quiet some variables in the data.frame and thus I don't want to write all > these names by hand, but instead create them on the fly. This approach has the > advantage that if there will be even more columns in the data.frame I don't > have to change the code. > > I've hence tried to construct a formula object and to pass that to aggregate: > > d <- expand.grid(a = factor(1:3), b = factor(LETTERS[1:2])) > d <- rbind(d,d,d) > d$y <- rnorm(18) > d$z <- rnorm(18) > mF <- as.formula(paste("cbind(", paste(names(d)[-(1:2)], collapse = ","), ") ~ > a + b", sep = "")) > > But if I try to pass that formula to aggregate > > aggregate(mF, d, mean) > > I get the following error: > > Error in m[[2L]][[2L]] : object of type 'symbol' is not subsettable > > But if I pass the formula directly: > > aggregate(cbind(y, z) ~ a + b, d, mean) > > Everything is working as expected. > > So I was wondering what went wrong? I know I could use a formula like . ~ a + > b instead and this would work fine, but I'm just interested in why the > outlined approach does not work as expected, and where my mistake lies? (that > means in particular I am not asking for a solution of how to get the thing > done - there are plenty of alternatives - but instead to understand why this > very approach does not work) > > Thanks for your help! > > Kind Regards, > > Thorn Thaler > Mathematician > > Applied Mathematics > Nestec Ltd, > Nestlé Research Center > PO Box 44 > CH-1000 Lausanne 26 > Phone: +41 21 785 8220 > Fax: +41 21 785 9486 > > ______________________________________________ > 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. > ______________________________________________ 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.
