Drop unused factor levels

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Description

Drop unused levels in a factor

Usage

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Arguments

x

object to be processed

reorder

should factor levels be reordered using reorder.factor?

...

additional arguments to reorder.factor

Details

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.

Value

Input object without unused levels.

Author(s)

Jim Rogers james.a.rogers@pfizer.com and Gregor Gorjanc

Examples

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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))

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