R: Construct a 'terms' Object from a Formula

terms.formula {stats}

R Documentation

Construct a `terms` Object from a Formula

Description

This function takes a formula and some optional arguments and constructs a terms object, which can then be used to construct a model.matrix.

Usage

## S3 method for class 'formula'
terms(x, specials = NULL, abb = NULL, data = NULL, neg.out = TRUE,
      keep.order = FALSE, simplify = FALSE, ...,
      allowDotAsName = FALSE)

Arguments

x

a formula.

specials

an optional character vector listing names of functions. Calls to these functions in the formula are marked as special in the terms object.

abb

Not implemented in R; deprecated.

data

a data frame from which the meaning of the special symbol . can be inferred. It is used only if there is a . in the formula.

neg.out

Not implemented in R; deprecated.

keep.order

a logical value indicating whether the terms should keep their positions. By default, when FALSE, the terms are reordered so that main effects come first, followed by the interactions, all second-order, all third-order and so on. Effects of a given order are kept in the order specified.

simplify

should the formula be expanded and simplified, the pre-1.7.0 behaviour?

...

further arguments passed to or from other methods.

allowDotAsName

normally . in a formula refers to the remaining variables contained in data. Exceptionally, . can be treated as a name for non-standard uses of formulae.

Details

Non-syntactic specials are supported since R 4.6.0. specials="pkg::name" marks as special calls `pkg::name`(...) (note backticks) and not calls pkg::name(...). The reverse was true prior to R 4.6.0, but that was undocumented and accidental.

Value

A terms object is returned. It is the re-ordered formula (unless keep.order = TRUE) with several attributes, see terms.object for details. In all cases variables within an interaction term in the formula are re-ordered by the ordering of the "variables" attribute, which is the order in which the variables occur in the formula.