getGroups.varFunc            package:nlme            R Documentation

Extract varFunc Groups

Description:

     This method function extracts the grouping factor associated with
     the variance function represented by 'object', if any is present.

Usage:

     ## S3 method for class 'varFunc':
     getGroups(object, form, level, data, sep)

Arguments:

  object: an object inheriting from class 'varFunc', representing a
          variance function structure.

    form: an optional formula with a conditioning expression on its
          right hand side (i.e. an expression involving the '|'
          operator). Defaults to 'formula(object)'.  Not used.

   level: a positive integer vector with the level(s) of grouping to be
          used when multiple nested levels of grouping are present.
          This argument is optional for most methods of this generic
          function and defaults to all levels of nesting.  Not used.

    data: a data frame in which to interpret the variables named in
          'form'. Optional for most methods.  Not used.

     sep: character, the separator to use between group levels when
          multiple levels are collapsed.  The default is ''/''.  Not
          used.

Value:

     if 'object' has a 'groups' attribute, its value is returned; else
     'NULL' is returned.

Author(s):

     Jose Pinheiro Jose.Pinheiro@pharma.novartis.com and Douglas Bates
     bates@stat.wisc.edu

Examples:

     data(Orthodont)
     vf1 <- varPower(form = ~ age | Sex)
     vf1 <- Initialize(vf1, Orthodont)
     getGroups(vf1)

