getGroups: Extract Grouping Factors from an Object
Description
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, sep)
Arguments
object
any object
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.
sep
character, the separator to use between group levels when
multiple levels are collapsed. The default is '/'.
Value
will depend on the method function used; see the appropriate documentation.
References
Pinheiro, J.C., and Bates, D.M. (2000) "Mixed-Effects Models
in S and S-PLUS", Springer, esp. pp. 100, 461.