getGroupsFormula {nlme} | R Documentation

## Extract Grouping Formula

### Description

The conditioning expression associated with `formula(object)` (i.e. the expression after the `|` operator) is returned either as a named list of one-sided formulas, or a single one-sided formula, depending on the value of `asList`. The components of the returned list are ordered from outermost to innermost level and are named after the grouping factor expression.

### Usage

    getGroupsFormula(object, asList, sep)

### Arguments

`object` | any object from which a formula can be extracted.
`asList` | an optional logical value. If `TRUE` the returned value with be a list of formulas; else, if `FALSE` the returned value will be a one-sided formula. Defaults to `FALSE`.
`sep` | character, the separator to use between group levels when multiple levels are collapsed. The default is `'/'`.

### Value

a one-sided formula, or a list of one-sided formulas, with the grouping structure associated with `formula(object)`. If no conditioning expression is present in `formula(object)` a `NULL` value is returned.

### Author(s)

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

### See Also

`getGroupsFormula.gls`, `getGroupsFormula.lmList`, `getGroupsFormula.lme`, `getGroupsFormula.reStruct`, `getGroups`

### Examples

    getGroupsFormula(y ~ x | g1/g2)

[Package nlme version 3.1-128 Index]