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.