R help - Oct 2008 - Turn factors to numeric

I am having some problems while trying to fit simple data.
I aggregated some data using:
data1 <- aggregate(data1$T2, list=(SOA=data1$SOA), mean)

unfortunatly this coerces my variable SOA into a factor. Therefore when a
afterwards try to fit a simple equation to my variable T2 using a formula on SOA
i get a error because SOA is a factor and that "*" is not meaningful
for factors...

nls(T2 ~ a + b*SOA, start=list(a=1,b=1), data=data1, trace=TRUE)

In fact SOA is a numeric variable (in my experiments it is the time that
passed!) so i would like to re-coerce it into a numeric variable to do the fit
or to find a method to do the fit even though SOA is a factor. Thanks a lot for
your help!

Best
Jokel
-- 
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R-FAQ 7.10:
http://cran.r-project.org/doc/FAQ/R-FAQ.html#How-do-I-convert-factors- 
to-numeric_003f

On Oct 9, 2008, at 6:59 AM, joseph kambeitz wrote:
> I am having some problems while trying to fit simple data.
> I aggregated some data using:
> data1 <- aggregate(data1$T2, list=(SOA=data1$SOA), mean)
>
> unfortunatly this coerces my variable SOA into a factor. Therefore  
> when a afterwards try to fit a simple equation to my variable T2  
> using a formula on SOA i get a error because SOA is a factor and  
> that "*" is not meaningful for factors...
>
> nls(T2 ~ a + b*SOA, start=list(a=1,b=1), data=data1, trace=TRUE)
>
> In fact SOA is a numeric variable (in my experiments it is the time  
> that passed!) so i would like to re-coerce it into a numeric  
> variable to do the fit or to find a method to do the fit even  
> though SOA is a factor. Thanks a lot for your help!
>
> Best
> Jokel
> -- 
> Ist Ihr Browser Vista-kompatibel? Jetzt die neuesten
>
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Haris Skiadas
Department of Mathematics and Computer Science
Hanover College