R: Transform an Allowable Formula for 'loglm' into one for...

denumerate {MASS} | R Documentation

## Transform an Allowable Formula for 'loglm' into one for 'terms'

### Description

`loglm` allows dimension numbers to be used in place of names in the formula. `denumerate` modifies such a formula into one that `terms` can process.

### Usage

    denumerate(x)

### Arguments

`x` | A formula conforming to the conventions of `loglm`, that is, it may allow dimension numbers to stand in for names when specifying a log-linear model.

### Details

The model fitting function `loglm` fits log-linear models to frequency data using iterative proportional scaling. To specify the model the user must nominate the margins in the data that remain fixed under the log-linear model. It is convenient to allow the user to use dimension numbers, 1, 2, 3, ... for the first, second, third, ..., margins in a similar way to variable names. As the model formula has to be parsed by `terms`, which treats `1` in a special way and requires parseable variable names, these formulae have to be modified by giving genuine names for these margin, or dimension numbers. `denumerate` replaces these numbers with names of a special form, namely `n` is replaced by `.vn`. This allows `terms` to parse the formula in the usual way.

### Value

A linear model formula like that presented, except that where dimension numbers, say `n`, have been used to specify fixed margins these are replaced by names of the form `.vn` which may be processed by `terms`.

### See Also

`renumerate`

### Examples

    denumerate(~(1+2+3)^3 + a/b)
    ## which gives ~ (.v1 + .v2 + .v3)^3 + a/b

[Package MASS version 7.3-45 Index]