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, ...)

### Arguments

`x` | a formula.
`specials` | which functions in the formula should be marked as special in the `terms` object.
`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.

### 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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