R: Extract Groups from a Data Frame

getGroups.data.frame {nlme}

R Documentation

Extract Groups from a Data Frame

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.

Usage

## S3 method for class 'data.frame'
getGroups(object, form, level, data, sep)

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.
`data`	unused
`sep`	character, the separator to use between group levels when multiple levels are collapsed. The default is `'/'`.

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)

José Pinheiro and Douglas Bates bates@stat.wisc.edu

References

Pinheiro, J.C., and Bates, D.M. (2000) "Mixed-Effects Models in S and S-PLUS", Springer, esp. pp. 100, 461.

Examples

getGroups(Pixel)
getGroups(Pixel, level = 2)

[Package nlme version 3.1-131 Index]