Extract Stratification Formula

DESCRIPTION:

This function is generic; method functions can be written to handle specific classes of objects. Classes which already have methods for this function include: corStruct, pdMat and reStruct .

USAGE:

getStrataFormula(object, ...) 

REQUIRED ARGUMENTS:

object
any object from which a formula representing a stratification variable can be extracted.
...
some methods for this generic function may require additional arguments.

VALUE:

a one-sided formula with the stratification variable associated with object . For most methods, if no stratification variable is present, a NULL value is returned.

SEE ALSO:

,

EXAMPLES:

pd1 <- pdStrat(~age, data = Orthodont, strata = ~ Sex) 
getStrataFormula(pd1)