[R] model fitting using by(): how to get fitted values?

Duncan Murdoch murdoch at stats.uwo.ca
Wed May 6 14:29:01 CEST 2009

On 06/05/2009 8:22 AM, xavier.chardon at free.fr wrote:
> Hi all,
> I'm doing nonlinear regressions on data with several factors. I want to fit say a logistic curve with different parameter values for each factor level. So I'm doing something like:
> tmp <- by( myData, list(myFactor1, myFactor2), function(x) nls(...) )
> It works fine. However, I could not find an easy way to retrieve fitted values. I can use fitted() on each element of tmp, but that gives me as many vectors as there are combinations of factor levels.

I think lapply() (or maybe sapply) will do what you want.  I haven't 
tried this, but it should be something like

lapply(tmp, fitted)

Duncan Murdoch

> I was thinking of using by() again, but I can't figure out how to write it properly.
> Any ideas?
> Thanks a lot,
> Xavier
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