Extract Groups from a Data Frame
Usage
getGroups(object, form, level)
Arguments
object
|
an object inheriting from class data.frame .
|
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. Defaults
to all levels of nesting.
|
Description
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.Value
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.Author(s)
Jose Pinheiro and Douglas BatesSee Also
getGroupsFormula
Examples
library(lme)
data(Pixel)
getGroups(Pixel)
getGroups(Pixel, level = 2)