Drop Levels of a Factor that Never Occur
Reform a factor so that only necessary levels are kept.
dropEmptyLevels(x)
x |
a factor or a vector to be converted to a factor. |
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.
A factor with the same values as x but with a possibly reduced set of levels.
Gordon Smyth
x <- factor(c("a","b"), levels=c("c","b","a"))
x
dropEmptyLevels(x)Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.