terms.object {stats} | R Documentation |

An object of class `terms`

holds information about a
model. Usually the model was specified in terms of a
`formula`

and that formula was used to determine the terms
object.

The object itself is simply the formula supplied to the call of
`terms.formula`

. The object has a number of attributes
and they are used to construct the model frame:

`factors` |
A matrix of variables by terms showing which variables
appear in which terms. The entries are 0 if the variable does not
occur in the term, 1 if it does occur and should be coded by
contrasts, and 2 if it occurs and should be coded via dummy
variables for all levels (as when an intercept or lower-order term
is missing). If there are no terms other than an intercept and offsets,
this is `numeric(0)` . |

`term.labels` |
A character vector containing the labels for each
of the terms in the model, except for offsets. Non-syntactic names
will be quoted by backticks. Note that these are after possible
re-ordering (unless argument `keep.order` was false). |

`variables` |
A call to `list` of the variables in the model. |

`intercept` |
Either 0, indicating no intercept is to be fit, or 1 indicating that an intercept is to be fit. |

`order` |
A vector of the same length as `term.labels`
indicating the order of interaction for each term |

`response` |
The index of the variable (in variables) of the response (the left hand side of the formula). Zero, if there is no response. |

`offset` |
If the model contains `offset` terms there
is an `offset` attribute indicating which variable(s) are offsets |

`specials` |
If a `specials` argument was given to
`terms.formula` there is a `specials` attribute, a
list of vectors (one for each specified special function) giving
numeric indices of the arguments of the list returned as the
`variables` attribute which contain these special functions. |

`dataClasses` |
optional. A named character vector giving the classes
(as given by `.MFclass` ) of the variables used in a fit. |

The object has class `c("terms", "formula")`

.

These objects are different from those found in S. In particular
there is no `formula`

attribute, instead the object is itself a
formula. Thus, the mode of a terms object is different as well.

Examples of the `specials`

argument can be seen in the
`aov`

and `coxph`

functions.

## use of specials (as used for gam() in packages mgcv and gam) (tf <- terms(y ~ x + x:z + s(x), specials = "s")) ## Note that the "factors" attribute has variables as row names ## and term labels as column names, both as character vectors. attr(tf, "specials") # index 's' variable(s) rownames(attr(tf, "factors"))[attr(tf, "specials")$s]

[Package *stats* version 2.2.1 Index]