[R] Grouped Regression

[Redding, Matthew]

HI All R Gurus, 

Please reply directly to this email if you have a suggestion, as I am not
currently an R-help member.

I would like to complete a non-linear regression with groups.  Having gone
down the path of completing such
things under GENSTAT, I would prefer to do it with R.

My example data set is...

 TimeTreat    ExtrVol2     SorbedT
         ET1        39.5       384.5
         ET1        78.7       305.2
         ET1       118.0       261.5
         ET1       157.6       233.7
         ET1       197.5       206.3
         ET2        37.5       422.1
         ET2        74.8       405.5
         ET2       112.0       382.6
         ET2       149.7       361.8
         ET2       187.4       347.7

To do a straightforward nls on the data, some code like this would be
necessary...

char<-read.table("O:/R_STH/L_TBA/P_IndSer/IntLive/Ilem_Research/Matt/Incubat
ion/Desorption Isotherms/RWork/DPIAds.txt", header=TRUE)
library(NLS)
test1<-nls(SorbedT~A + B/(1 + D*ExtrVol2), data=char, start=list(A=200,B=80,
D=0.003),trace=TRUE)
summary(test1)


Given this code, How do I alter it to group regression based on the factor
TimeTreat, and provide a comparison of the 
results?

Thanks, 

Matt Redding



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