getGroups.varFunc            package:nlme            R Documentation

_E_x_t_r_a_c_t _v_a_r_F_u_n_c _G_r_o_u_p_s

_D_e_s_c_r_i_p_t_i_o_n:

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

_U_s_a_g_e:

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

_A_r_g_u_m_e_n_t_s:

  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.

_V_a_l_u_e:

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

_A_u_t_h_o_r(_s):

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

_E_x_a_m_p_l_e_s:

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

