update.formula {stats}R Documentation

Model Updating

Description

update.formula is used to update model formulae. This typically involves adding or dropping terms, but updates can be more general.

Usage

## S3 method for class 'formula':
update(old, new, ...)

Arguments

old a model formula to be updated.
new a formula giving a template which specifies how to update.
... further arguments passed to or from other methods.

Details

The function works by first identifying the left-hand side and right-hand side of the old formula. It then examines the new formula and substitutes the lhs of the old formula for any occurence of "." on the left of new, and substitutes the rhs of the old formula for any occurence of "." on the right of new.

Value

The updated formula is returned.

See Also

terms, model.matrix.

Examples

update(y ~ x,    ~ . + x2) #> y ~ x + x2
update(y ~ x, log(.) ~ . ) #> log(y) ~ x

[Package stats version 2.1.0 Index]