stats (version 3.3.3)

terms.formula: Construct a terms Object from a Formula

Description

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

Usage

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

Arguments

x

a formula.

specials

which functions in the formula should be marked as special in the terms object? A character vector or NULL.

abb

Not implemented in R.

data

a data frame from which the meaning of the special symbol . can be inferred. It is unused if there is no . in the formula.

neg.out

Not implemented in R.

keep.order

a logical value indicating whether the terms should keep their positions. If 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.

Value

A terms.object object is returned. The object itself is the re-ordered (unless keep.order = TRUE) formula. 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.

Details

Not all of the options work in the same way that they do in S and not all are implemented.

See Also

terms, terms.object