Each variable named in the expression after the | operator on
the right hand side of form is evaluated in object. If
more than one variable is indicated in level they are combined
into a data frame; else the selected variable is returned as a vector.
When multiple grouping levels are defined in form and
level > 1, the levels of the returned factor are obtained by
pasting together the levels of the grouping factors of level greater
or equal to level, to ensure their uniqueness.
# S3 method for data.frame
getGroups(object, form, level, data, sep)either a data frame with columns given by the grouping factors
indicated in level, from outer to inner, or, when a single
level is requested, a factor representing the selected grouping
factor.
an object inheriting from class data.frame.
an optional formula with a conditioning expression on its
right hand side (i.e. an expression involving the |
operator). Defaults to formula(object).
a positive integer vector with the level(s) of grouping to be used when multiple nested levels of grouping are present. Defaults to all levels of nesting.
unused
character, the separator to use between group levels when
multiple levels are collapsed. The default is '/'.
José Pinheiro and Douglas Bates bates@stat.wisc.edu
Pinheiro, J.C., and Bates, D.M. (2000) "Mixed-Effects Models in S and S-PLUS", Springer, esp. pp. 100, 461.
getGroupsFormula
getGroups(Pixel)
getGroups(Pixel, level = 2)
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