The conditioning expression associated with
formula(object)
(i.e. an expression after the `|' operator) is returned either as
a named list of one-sided formulas, 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.
USAGE:
getGroupsFormula(object, asList)
REQUIRED ARGUMENTS:
object
any object from which a formula can be extracted.
OPTIONAL ARGUMENTS:
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.
VALUE:
a one-sided formula, or a list of one-sided formulas, with the
grouping structure associated with
formula(object). If no
conditioning expression is present in
formula(object) a
NULL
value is returned.