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

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## 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.

See Also

terms, terms.object

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