getGroups.gls {nlme} | R Documentation

## Extract gls Object Groups

### Description

If present, the grouping factor associated to the correlation structure for the linear model represented by `object` is extracted.

### Usage

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

### Arguments

`object` | an object inheriting from class `gls`, representing a generalized least squares fitted linear model.
`form` | an optional formula with a conditioning expression on its right hand side (i.e. an expression involving the `|` operator). Defaults to `formula(object)`. Not used.
`level` | a positive integer vector with the level(s) of grouping to be used when multiple nested levels of grouping are present. This argument is optional for most methods of this generic function and defaults to all levels of nesting. Not used.
`data` | a data frame in which to interpret the variables named in `form`. Optional for most methods. Not used.
`sep` | character, the separator to use between group levels when multiple levels are collapsed. The default is `'/'`. Not used.

### Value

if the linear model represented by `object` incorporates a correlation structure and the corresponding `corStruct` object has a grouping factor, a vector with the group values is returned; else, `NULL` is returned.

### Author(s)

Jose Pinheiro Jose.Pinheiro@pharma.novartis.com and Douglas Bates bates@stat.wisc.edu

### See Also

`gls`, `corClasses`

### Examples

    data(Ovary)
    fm1 <- gls(follicles ~ sin(2*pi*Time) + cos(2*pi*Time), Ovary,
               correlation = corAR1(form = ~ 1 | Mare))
    getGroups(fm1)

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