# fixed formula part: f <- dat ~ a0 * exp(-S*(x - 250)) + K # convert to character f <- as.character(f) # component: C <- "(p0*exp(-0.5*((x-p1)/p2)^2))" # number of components (defined randomly): n <- sample(1:3, 1) C <- rep(C, n) # collapse: C <- paste(C, collapse = "+") # combine f <- paste(f[2], f[1], f[3], "+", C) as.formula(f) # hope this helps. # best, s
On 21 November 2014 at 14:23, philippe massicotte <pmassico...@hotmail.com> wrote: > Hi everyone. > > I have a non-linear model specified as this (6 variables, a0, S, K, p0, p1, > p2): > > fit <- nlsLM(formula = dat ~ a0 * exp(-S*(x - 250)) + K + ( C ) ) > > where C = (p0*exp(-0.5*((x-p1)/p2)^2)) > > The problem is that I do not know in advance how many component (C) I will > have in the model. That means It could be: > > nlsLM(formula = dat ~ a0 * exp(-S*(x - 250)) + K + ( > (p0*exp(-0.5*((x-p1)/p2)^2)) ) ) > > or > > nlsLM(formula = dat ~ a0 * exp(-S*(x - 250)) + K + ( > (p0*exp(-0.5*((x-p1)/p2)^2)) ) + ( (p0b*exp(-0.5*((x-p1b)/p2b)^2)) )) > > or > > > nlsLM(formula = dat ~ a0 * exp(-S*(x - 250)) + K + ( > (p0*exp(-0.5*((x-p1)/p2)^2)) ) + ( (p0b*exp(-0.5*((x-p1b)/p2b)^2)) + ( > (p0c*exp(-0.5*((x-p1c)/p2c)^2)))) > > So I was wondering if it was possible to dynamically build the formula that I > will use in my model? The first part of my model will always be "a0 * > exp(-S*(x - 250)) + K", I just want to add a certain number of "components" > dynamically. > > I guess it will be related with "reformulate()" but I can't not find how to > make it works. > > Thank you for your help, > Philippe > > > [[alternative HTML version deleted]] > > ______________________________________________ > 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.
