This method function extracts the grouping factor associated with
object, if any is present.
Usage
# S3 method for corStruct
getGroups(object, form, level, data, sep)
Arguments
object
an object inheriting from class corStruct
representing a correlation structure.
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.
level
this argument is included to make the method function
compatible with the generic and is not used.
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.
sep
character, the separator to use between group levels when
multiple levels are collapsed. The default is '/'.
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.