R: Reorder Levels of a Factor

reorder.default {stats} | R Documentation

## 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

    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 deepayan.sarkar@r-project.org

### See Also

`reorder.dendrogram`, `levels`, `relevel`.

### Examples

    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")

[Package stats version 4.0.5 Index]