getGroups.data.frame          package:nlme          R Documentation

Extract Groups from a Data Frame

Description:

     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.

Usage:

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

Arguments:

  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 ''/''.

Value:

     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.

Author(s):

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

References:

     Pinheiro, J.C., and Bates, D.M. (2000) "Mixed-Effects Models in S
     and S-PLUS", Springer, esp. pp. 100, 461.

See Also:

     'getGroupsFormula'

Examples:

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

