R: Modify Terms Objects

delete.response {stats}

R Documentation

Modify Terms Objects

Description

delete.response returns a terms object for the same model but with no response variable.

drop.terms removes variables from the right-hand side of the model. There is also a "[.terms" method to perform the same function (with keep.response=TRUE).

reformulate creates a formula from a character vector.

Usage

delete.response(termobj)

reformulate(termlabels, response = NULL, intercept = TRUE)

drop.terms(termobj, dropx = NULL, keep.response = FALSE)

Arguments

`termobj`	A `terms` object
`termlabels`	character vector giving the right-hand side of a model formula. Cannot be zero-length.
`response`	character string, symbol or call giving the left-hand side of a model formula, or `NULL`.
`intercept`	logical: should the formula have an intercept? New in R 2.13.0.
`dropx`	vector of positions of variables to drop from the right-hand side of the model.
`keep.response`	Keep the response in the resulting object?

Value

delete.response and drop.terms return a terms object.

reformulate returns a formula.

Examples

ff <- y ~ z + x + w
tt <- terms(ff)
tt
delete.response(tt)
drop.terms(tt, 2:3, keep.response = TRUE)
tt[-1]
tt[2:3]
reformulate(attr(tt, "term.labels"))

## keep LHS :
reformulate("x*w", ff[[2]])
fS <- surv(ft, case) ~ a + b
reformulate(c("a", "b*f"), fS[[2]])

stopifnot(identical(      ~ var, reformulate("var")),
          identical(~ a + b + c, reformulate(letters[1:3])),
          identical(  y ~ a + b, reformulate(letters[1:2], "y"))
         )