This method function extracts the grouping factor associated with
object
, if any is present.
USAGE:
getGroups(object, form, data, level)
REQUIRED ARGUMENTS:
object
an object inheriting from class
corStruct
representing a correlation structure.
OPTIONAL ARGUMENTS:
form
this argument is included to make the method function
compatible with the generic. It will be assigned the value of
formula(object) and should not be modified.
data
an optional data frame in which to evaluate the variables
defined in
form, in case
object is not initialized and
the grouping factor needs to be evaluated.
level
this argument is included to make the method function
compatible with the generic and is not used.
VALUE:
if a grouping factor is present in the correlation structure
represented by
object, the function returns the corresponding
factor vector; else the function returns
NULL.