R: Contrast Matrices

contrast.bayes {arm} | R Documentation

## Contrast Matrices

### Description

Return a matrix of contrasts used in `bayesglm`.

### Usage

    contr.bayes.unordered(n, base = 1, contrasts = TRUE)
    contr.bayes.ordered (n, scores = 1:n, contrasts = TRUE)

### Arguments

`n` | a vector of levels for a factor, or the number of levels.
`base` | an integer specifying which group is considered the baseline group. Ignored if `contrasts` is `FALSE`.
`contrasts` | a logical indicating whether contrasts should be computed.
`scores` | the set of values over which orthogonal polynomials are to be computed.

### Details

These functions are adapted from `contr.treatment` and `contr.poly` in `stats` package. The purpose for these functions are to keep the baseline levels of categorical variables and thus to suit the use of `bayesglm`.

`contr.bayes.unordered` is equivalent to `contr.treatment` whereas `contr.bayes.ordered` is equivalent to `contr.poly`.

### Author(s)

Yu-Sung Su suyusung@tsinghua.edu.cn

### See Also

`C`, `contr.helmert`, `contr.poly`, `contr.sum`, `contr.treatment`; `glm`, `aov`, `lm`, `bayesglm`.

### Examples

     cat.var <- rep(1:3, 5)
     dim(contr.bayes.unordered(cat.var))
     # 15*15 baseline level kept!
     dim(contr.treatment(cat.var))
     # 15*14

[Package arm version 1.9-3 Index]