Dennis, this works perfectly! Thanks, Otto
On Fri, Mar 11, 2011 at 2:08 PM, Dennis Murphy <djmu...@gmail.com> wrote: > Hi: > > Perhaps something like > > f1(x, y) * I(z > 0) + f2(x, y) * I(z <= 0) ?? > > HTH, > Dennis > > On Fri, Mar 11, 2011 at 3:10 AM, Otto Kässi <otto.ka...@gmail.com> wrote: >> >> Dear r-helpers, >> >> This might be an elementary question, but I have a hard time getting >> my head around it, so all help is much appreciated. >> >> I am working on a nonlinear regression model of the form >> >> if z > 0 >> y = f1(x,y), >> else >> y = f2(x,t) . >> >> In other words, the functional form of f(.) changes according to some >> criteria z. Natural approach would be to fit two models, i.e. >> model1 <- nlm(y ~ ..., data=data[data$z > 0,]), >> model2 <- nlm(y ~ ..., data=data[data$z <= 0,]). >> But this is unfeasible since both models contain the same variable x >> and I would like to estimate the coefficient on x using both subsets >> of the data. >> >> My first shot would be to do something like this: >> formula <- ifelse(z > 0, "y ~ f(x,y).", "y ~ f(x,t)") >> nlm(formula, data=data) >> >> .. but preliminary testing indicates that this might not work. The >> coefficient on t does not get estimated. >> >> Thanks in advance for all helpful suggestions! >> >> With kind regards, >> Otto >> >> ---- >> Otto Kassi >> University of Helsinki >> Dept. of Economics >> >> ______________________________________________ >> 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.
