On Mon, 2009-12-21 at 13:20 -0500, John Tillinghast wrote:
> I'm trying to build a model with an overall smooth function for all
> the data, plus an additional smooth function for *some* of the data.
> If "ind" is my indicator variable (0 for some x, 1 for others), I
> imagined I could write it like this:
>
> gam.obj <- gam(y ~ s(x) + ind*s(x))
>
> but this does not work.
>
> Does mgcv have a way of doing this? If not directly, is there a
> reasonable workaround?
>
If I understand you correctly, yes. see ?s and argument 'by'. Something
like:
## some dummy data
dat <- data.frame(y=rnorm(100), x=c(rnorm(50,5), rnorm(50)),
ind = rep(c(1,0), each = 50))
## fit model
mod <- gam(y ~ s(x) + s(x, by = ind), data = dat)
This works when ind is a simple indicator, but if you have more levels
(as a factor), by = ind will fit a separate smooth to each level of ind.
HTH
G
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Dr. Gavin Simpson [t] +44 (0)20 7679 0522
ECRC, UCL Geography, [f] +44 (0)20 7679 0565
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