# Re: [R] How to put factor variables in an nls formula ?

From: Douglas Bates <dmbates_at_gmail.com>
Date: Sat 20 Aug 2005 - 00:12:40 EST

On 8/18/05, François Morneau <francois.morneau@cirad.fr> wrote:
> Hello,
>
> I want to fit a Gompertz model for tree diameter growth that depends on a 4
> levels edaphic factor ('Drain') and I don't manage to introduce the factor
> variable in the formula.
> Dinc is the annual diameter increment and D is the Diameter.
>
> >treestab
> > Dinc D Drain
> [1,] 0.03 26.10 2
> [2,] 0.04 13.05 1
> [3,] 0.00 24.83 1
> [4,] 0.00 15.92 4
> [5,] 0.00 12.25 4
> [6,] 0.00 11.78 4
> [7,] 0.00 16.87 4
> [8,] 0.00 15.12 4
> [9,] -0.01 13.53 4
> [10,] 0.04 16.55 3
> [11,] 0.025 16.07 3
> [12,] 0.00 30.24 3
> [13,] 0.06 15.28 2
> etc…
> >contrasts(Drain)<-contr.sum(4)
> >mymodel<-nls(Dinc~r*(1+Drain)*D*log(Asym/D), data=treestab, start(r=0.05,
> Asym=40))
>
> Error in numericDeriv(form[[3]], names(ind), env) :
> Missing value or an infinity produced when evaluating the model
> 1: + not meaningful for factors in: Ops.factor(1, Drain)
> 2: + not meaningful for factors in: Ops.factor(1, Drain)

It is not clear to me what you are trying to do. Can you give us a bit more information such as how many parameter estimates you expect to obtain and what they would represent?

>
> Do I need to use another function instead of nls to correctly include the
> factor 'Drain' ?
>
> Thanks,
>
> François
>
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