getGroups.data.frame          package:nlme          R Documentation

_E_x_t_r_a_c_t _G_r_o_u_p_s _f_r_o_m _a _D_a_t_a _F_r_a_m_e

_D_e_s_c_r_i_p_t_i_o_n:

     Each variable named in the expression after the '|' operator on
     the right hand side of 'form' is evaluated in 'object'. If more
     than one variable is indicated in 'level' they are combined into a
     data frame; else the selected variable is returned as a vector.
     When multiple grouping levels are defined in 'form' and 'level >
     1', the levels of the returned factor are obtained by pasting
     together the levels of the grouping factors of level greater or
     equal to 'level', to ensure their uniqueness.

_U_s_a_g_e:

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

_A_r_g_u_m_e_n_t_s:

  object: an object inheriting from class 'data.frame'.

    form: an optional formula with a conditioning expression on its
          right hand side (i.e. an expression involving the '|'
          operator). Defaults to 'formula(object)'.

   level: a positive integer vector with the level(s) of grouping to be
          used when multiple nested levels of grouping are present.
          Defaults to all levels of nesting.

    data: unused

     sep: character, the separator to use between group levels when
          multiple levels are collapsed.  The default is ''/''.

_V_a_l_u_e:

     either a data frame with columns given by the grouping factors
     indicated in 'level', from outer to inner, or, when a single level
     is requested, a factor representing the selected grouping factor.

_A_u_t_h_o_r(_s):

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

_S_e_e _A_l_s_o:

     'getGroupsFormula'

_E_x_a_m_p_l_e_s:

     getGroups(Pixel)
     getGroups(Pixel, level = 2)

