R: Reorder Levels of Factor

relevel {base} | R Documentation

## Reorder Levels of Factor

### Description

The levels of a factor are re-ordered so that the level specified by `ref` is first and the others are moved down. This is useful for `contr.treatment` contrasts which take the first level as the reference.

### Usage

    relevel(x, ref, ...)

### Arguments

`x` | An unordered factor.
`ref` | The reference level.
`...` | Additional arguments for future methods.

### Value

A factor of the same length as `x`.

### Author(s)

B. D. Ripley

### See Also

`factor`, `contr.treatment`

### Examples

    data(warpbreaks)
    warpbreaks$tension <- relevel(warpbreaks$tension, ref="M")
    summary(lm(breaks ~ wool + tension, data=warpbreaks))

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