

   EExxttrraacctt GGrroouuppiinngg FFoorrmmuullaa

        getGroupsFormula(object, asList)

   AArrgguummeennttss::

     object: any object from which a formula can be extracted.

     asList: an optional logical value. If `TRUE' the returned
             value with be a list of formulas; else, if `FALSE'
             the returned value will be a one-sided formula.
             Defaults to `FALSE'.

   DDeessccrriippttiioonn::

        The conditioning expression associated with `for-
        mula(object)' (i.e. an expression after a `|' operator)
        is returned either as a named list of one-sided formu-
        las, or a single one-sided formula, depending  on the
        value of `asList'. The components of the returned list
        are ordered from outermost to innermost level and are
        named after the grouping factor expression.

   VVaalluuee::

        a one-sided formula, or a list of one-sided formulas,
        with the grouping structure associated with `for-
        mula(object)'. If no conditioning expression is present
        in `formula(object)' a `NULL' value is returned.

   AAuutthhoorr((ss))::

        Jose Pinheiro and Douglas Bates

   SSeeee AAllssoo::

        `getGroups'

   EExxaammpplleess::

        library(lme)
        getGroupsFormula(y ~ x | g1/g2)

