Formula with dynamic number of variables
# 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
<pmassicotte at 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
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