formula
Define or Extract a Model Formula
Description
Defines or extracts a formula object.
This function is an S Version 3 generic (see Methods). A generic
function adapts its action to match the class of an object by calling
a method function specified for that class. You can create a method
function to handle specific S Version 3 classes of data. Method
functions for the classes data.frame, formula,
lm, nls, and terms are included.
Usage
formula(x, ...)
as.formula(object, env = parent.frame())
## Default S3 method:
formula(x, env = parent.frame(), ...)
## S3 method for class 'call':
formula(x, env = parent.frame(), ...)
## S3 method for class 'character':
formula(x, env = parent.frame(), ...)
## S3 method for class 'data.frame':
formula(x, ..., env = parent.frame())
## S3 method for class 'formula':
formula(x, ...)
## S3 method for class 'lm':
formula(x, ...)
## S3 method for class 'nls':
formula(x, ...)
## S3 method for class 'terms':
formula(x, ...)
Arguments
| x |
either a formula expression--that is, a call to the tilde (~)
operator or a character string that could be parsed to make such a
call--or an object that contains a previously constructed formula,
such as a fitted model or a terms object.
As a special case, formula(data.frame will construct a formula
in which the response is the first column of the data.frame and the
other columns are additive predictors.
|
| object |
For historical reasons as.formula calls its first argument
object but it is treated the same as x in formula.
|
| env |
The environment to assign to the formula. The modelling functions
will look up names from the formula in this environment.
(Names not found in that environment, or its ancestral environments,
will be looked up in the environment of the caller of the modelling
function.)
|
Value
formula returns an object of class "formula", essentially the call to
the tilde (~) operator along with an attribute, ".Environment",
that gives the environment in which the formula was constructed.
The return value for as.formula differs in that if its
object argument inherits from class formula it
returns it, as-is. Otherwise it returns formula(object).
See Also
Examples
Fuel ~ Weight + Disp.
formula(lm(Fuel ~ Weight + Type * Disp., data=Sdatasets::fuel.frame))
formula(Sdatasets::fuel.frame)