factor.scope              package:stats              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.

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"

