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 terms from the right-hand side of the model, optionally keeping the response. There is also a [.terms method performing a complementary operation: it extracts terms, always keeping the response.

reformulate creates a formula from a character vector. If length(termlabels) > 1, its elements are concatenated with +. Non-syntactic names (e.g. containing spaces or special characters; see make.names) must be protected with backticks (see examples). A non-parseable response still works for now, back compatibly, with a deprecation warning.

Usage

delete.response(termobj)

reformulate(termlabels, response = NULL, intercept = TRUE, env = parent.frame())

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`	a character string, symbol or call giving the left-hand side of a model formula, or `NULL`.
`intercept`	logical: should the formula have an intercept?
`env`	the `environment` of the `formula` returned.
`dropx`	a numeric vector indexing `labels(termobj)` (that is, the `"term.labels"` attribute of `termobj`), indicating terms to be dropped from the right-hand side of the model, or `NULL` (default) to keep all terms.
`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]])

## using non-syntactic names:
reformulate(c("`P/E`", "`% Growth`"), response = as.name("+-"))

x <- c("a name", "another name")
tryCatch( reformulate(x), error = function(e) "Syntax error." )
## rather backquote the strings in x :
reformulate(sprintf("`%s`", x))

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