This function is generic; method functions can be written to handle
specific classes of objects. Classes which already have methods for
this function include
corStruct,
data.frame,
gls
,
lme,
lmList, and
varFunc.
USAGE:
getGroups(object, form, level, data)
REQUIRED ARGUMENTS:
object
any object
OPTIONAL ARGUMENTS:
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. This
argument is optional for most methods of this generic function and
defaults to all levels of nesting.
data
a data frame in which to interpret the variables named in
form. Optional for most methods.
VALUE:
will depend on the method function used; see the appropriate documentation.