Extract varFunc Covariate

This method function extracts the covariate(s) associated with the variance function represented by object, if any is present.

# S3 method for class 'varFunc'
getCovariate(object, form, data)

Arguments

object

an object inheriting from class varFunc, representing a variance function structure.

form

an optional formula specifying the covariate to be evaluated in object. Defaults to formula(object).

data

some methods for this generic require a data object. Not used in this method.

Value

if object has a covariate attribute, its value is returned; else NULL is returned.

Author

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

See also

covariate<-.varFunc

Examples

vf1 <- varPower(1.1, form = ~age)
covariate(vf1) <- Orthodont[["age"]]
getCovariate(vf1)
#>   [1]  8 10 12 14  8 10 12 14  8 10 12 14  8 10 12 14  8 10 12 14  8 10 12 14  8
#>  [26] 10 12 14  8 10 12 14  8 10 12 14  8 10 12 14  8 10 12 14  8 10 12 14  8 10
#>  [51] 12 14  8 10 12 14  8 10 12 14  8 10 12 14  8 10 12 14  8 10 12 14  8 10 12
#>  [76] 14  8 10 12 14  8 10 12 14  8 10 12 14  8 10 12 14  8 10 12 14  8 10 12 14
#> [101]  8 10 12 14  8 10 12 14