dropEmptyLevels {edgeR} | R Documentation

## Drop Levels of a Factor that Never Occur

### Description

Reform a factor so that only necessary levels are kept.

### Usage

    dropEmptyLevels(x)

### Arguments

`x` | a factor or a vector to be converted to a factor.

### Details

In general, the levels of a factor, `levels(x)`, may include values that never actually occur. This function drops any levels of that do not occur.

If `x` is not a factor, then the function returns `factor(x)`. If `x` is a factor, then the function returns the same value as `factor(x)` or `x[,drop=TRUE]` but somewhat more efficiently.

### Value

A factor with the same values as `x` but with a possibly reduced set of levels.

### Author(s)

Gordon Smyth

### See Also

`factor`.

### Examples

    x <- factor(c("a","b"), levels=c("c","b","a"))
    x
    dropEmptyLevels(x)

[Package edgeR version 3.34.1 Index]