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. The terms object 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`	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.

Details

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

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.