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.
# S3 method for formula
terms(x, specials = NULL, abb = NULL, data = NULL, neg.out = TRUE,
keep.order = FALSE, simplify = FALSE, …,
allowDotAsName = FALSE)a formula.
which functions in the formula should be marked as
special in the terms object? A character vector or NULL.
Not implemented in R.
a data frame from which the meaning of the special symbol
. can be inferred. It is unused if there is no . in
the formula.
Not implemented in R.
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.
should the formula be expanded and simplified, the pre-1.7.0 behaviour?
further arguments passed to or from other methods.
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.
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.
Not all of the options work in the same way that they do in S and not all are implemented.