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.

### See Also

`getGroupsFormula`

### Examples

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

[Package nlme version 3.1-118 Index]