factor.scope              package:base              R Documentation

Compute Allowed Changes in Adding to or Dropping from a Formula

Description:

     `add.scope' and `drop.scope' compute those terms that can be
     individually added to or dropped from a model while respecting the
     hierarchy of terms.

Usage:

     add.scope(terms1, terms2)
     drop.scope(terms1, terms2)
     factor.scope(factor, scope)

Arguments:

  terms1: the terms or formula for the base model.

  terms2: the terms or formula for the upper (`add.scope') or lower
          (`drop.scope') scope. If missing for `drop.scope' it is taken
          to be the null formula, so all terms (except any intercept)
          are candidates to be dropped.

  factor: the `"factor"' attribute of the terms of the base object.

   scope: a list with one or both components `drop' and `add' giving
          the `"factor"' attribute of the lower and upper scopes
          respectively.

Details:

     `factor.scope' is not intended to be called directly by users.

Value:

     For `add.scope' and `drop.scope' a character vector of terms
     labels. For `factor.scope', a list with components `drop' and
     `add', character vectors of terms labels.

Author(s):

     B.D. Ripley

See Also:

     `add1', `drop1', `aov', `lm'

Examples:

     add.scope( ~ a + b + c + a:b,  ~ (a + b + c)^3)
     # [1] "a:c" "b:c"
     drop.scope( ~ a + b + c + a:b)
     # [1] "c"   "a:b"

