basic question on getGroups for lme analyses

As far as I know GetGroups is designed to extract grouping factors from an 
object, not to create them . To do so you can either specify your hierarchy 
in the random argument of your lme model .i.e. m1<-lme(distance~age, 
data=Orthodont, random = ~age|Subject)

or you can also create grouped data using groupedData.i.e:

groupedData( distance ~ age | Subject,
                   data = as.data.frame( Orthodont ),
                   FUN = mean,
                   outer = ~ Sex,
                   labels = list( x = "Age",
                     y = "Distance from pituitary to pterygomaxillary 
fissure" ),
                   units = list( x = "(yr)", y = "(mm)") )

     plot( Orth.new )         # trellis plot by Subject

     formula( Orth.new )      # extractor for the formula
     gsummary( Orth.new )     # apply summary by Subject
     fm1 <- lme( Orth.new )   # fixed and groups formulae extracted from 
object
     Orthodont2 <- update(Orthodont, FUN = mean)

From: "Jose A. Andres" <joseandres at uvigo.es>
To: <r-help at stat.math.ethz.ch>
Subject: [R] basic question on getGroups for lme analyses
Date: Thu, 22 May 2003 14:02:44 +0200

Hi all!

I am working on a nested lme model with one fixed effect ("treatment", 
which 3 levels) and two random effects for "Individuals" (four of them) 
within "treatment" and "replicate -2 levels-" within "individual" within 
"treatment". For doing so, I?ve been trying to create a factor for 
Individual%in%Treatment, say IT
by

Hongos$IT=getGroups(~1|Treatment/Individual, data=hongos1, level=4)

but I got the following error:

Error in getGroups(~1 | Treatment/Individual, data = hongos1, level = 4) :
        no applicable method for "getGroups"

I've been trying some other things but nothing seem to work, probably 
because I cannot fully understand how o use the getGroups command. Any 
suggestions?

Thanks a lot!

/Jose



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