# reorder.factor: Reorder Levels of a Factor

## Description

`reorder` is a generic function. The `"default"` method treats its first argument as a categorical variable, and reorders its levels based on the values of a second variable, usually numeric.

## Usage

 ```1 2 3 4 5``` ```reorder(x, ...) ## Default S3 method: reorder(x, X, FUN = mean, ..., order = is.ordered(x)) ```

## Arguments

 `x` an atomic vector, usually a `factor` (possibly ordered). The vector is treated as a categorical variable whose levels will be reordered. If `x` is not a factor, its unique values will be used as the implicit levels. `X` a vector of the same length as `x`, whose subset of values for each unique level of `x` determines the eventual order of that level. `FUN` a `function` whose first argument is a vector and returns a scalar, to be applied to each subset of `X` determined by the levels of `x`. `...` optional: extra arguments supplied to `FUN` `order` logical, whether return value will be an ordered factor rather than a factor.

## Details

This, as `relevel()`, is a special case of simply calling `factor(x, levels = levels(x)[....])`.

## Value

A factor or an ordered factor (depending on the value of `order`), with the order of the levels determined by `FUN` applied to `X` grouped by `x`. The levels are ordered such that the values returned by `FUN` are in increasing order. Empty levels will be dropped.

Additionally, the values of `FUN` applied to the subsets of `X` (in the original order of the levels of `x`) is returned as the `"scores"` attribute.

## Author(s)

Deepayan Sarkar [email protected]

`reorder.dendrogram`, `levels`, `relevel`.
 ```1 2 3 4 5 6 7``` ```require(graphics) bymedian <- with(InsectSprays, reorder(spray, count, median)) boxplot(count ~ bymedian, data = InsectSprays, xlab = "Type of spray", ylab = "Insect count", main = "InsectSprays data", varwidth = TRUE, col = "lightgray") ```