edgeR (version 3.14.0)

dropEmptyLevels: 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.

Value

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

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.

See Also

factor.

Examples

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