R: Compute Allowed Changes in Adding to or Dropping from a Formula

factor.scope {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"

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