getGroups.corStruct {nlme} | R Documentation

## Extract corStruct Groups

### Description

This method function extracts the grouping factor associated with `object`, if any is present.

### Usage

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

### Arguments

`object` | an object inheriting from class `corStruct` representing a correlation structure.
`form` | this argument is included to make the method function compatible with the generic. It will be assigned the value of `formula(object)` and should not be modified.
`level` | this argument is included to make the method function compatible with the generic and is not used.
`data` | an optional data frame in which to evaluate the variables defined in `form`, in case `object` is not initialized and the grouping factor needs to be evaluated.
`sep` | character, the separator to use between group levels when multiple levels are collapsed. The default is `'/'`.

### Value

if a grouping factor is present in the correlation structure represented by `object`, the function returns the corresponding factor vector; else the function returns `NULL`.

### Author(s)

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

### See Also

`getGroups`

### Examples

    cs1 <- corAR1(form = ~ 1 | Subject)
    getGroups(cs1, data = Orthodont)

[Package nlme version 3.1-131 Index]