terms.formula             package: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'

