Drop unused factor levels
Drop unused levels in a factor
drop.levels(x, reorder=TRUE, ...)
x |
object to be processed |
reorder |
should factor levels be reordered using
|
... |
additional arguments to |
drop.levels is a generic function, where default method does
nothing, while method for factor s drops all unused levels. Drop
is done with x[, drop=TRUE].
There are also convenient methods for list and data.frame,
where all unused levels are dropped in all factors (one by one) in a
list or a data.frame.
Input object without unused levels.
Jim Rogers james.a.rogers@pfizer.com and Gregor Gorjanc
f <- factor(c("A", "B", "C", "D"))[1:3]
drop.levels(f)
l <- list(f=f, i=1:3, c=c("A", "B", "D"))
drop.levels(l)
df <- as.data.frame(l)
str(df)
str(drop.levels(df))Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.