relevel
Reorder Levels of Factor

### Description

Reorders the levels of an existing factor. The reference level is moved to the first position and the others retain their original order.

### Usage

    relevel(x, ref, ...)

### Arguments

x | a factor.
ref | a character string matching a string in levels(x), or an integer index into levels(x) to specify which level to use as the reference level.
... | reserved for future use.

### Details

This is a generic function. Some S3 methods are implemented for class factor, ordered, and default. An error is returned for ordered and default.
Value
returns a factor with the same length as x, where the first level is the desired reference level.
See Also
factor, levels, contr.treatment.
Examples

    dose <- factor(c(.1, .4, 1.2, .1, .4, 1.2, .4))
    response <- c(10, 15, 29, 9, 13, 33, 14)
    dose
    dose2_ <- relevel(dose, "0.4") # move second level, "0.4", to front
    dose2_
    relevel(dose, 2) # alternate way to do same thing
    tapply(response, list(dose=dose2_), mean) # mean response by dose
    # The following assumes getOption("contrasts")[1] == "contr.treatment"
    coefficients(lm(response ~ dose)) # effects relative to dose=0.1
    coefficients(lm(response ~ dose2_)) # effects relative to dose=0.4

Package stats version 6.1.5-18
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