[R] levels of factor when subsetting the factor

Liaw, Andy andy_liaw at merck.com
Tue Sep 12 17:31:58 CEST 2006

You have at least two choices:

R> factor(fact[1:6])
[1] A A A B B B
Levels: A B
R> fact[1:6, drop=TRUE]
[1] A A A B B B
Levels: A B


From: Afshartous, David
> All,
> When I take a subset of a factor the reduced factor still 
> maintains all
> the original levels of the factor when say forming the key in a plot.
> The data is correct, but the variable still "remembers" the original
> levels.  See below for reproducible code.  Does anyone know how to fix
> this?
> cheers,
> dave
> fact = as.factor(c(rep("A", 3),rep("B", 3), rep("C", 3)))
> new.fact = fact[1:6]
> > new.fact
> [1] A A A B B B
> Levels: A B C    ## should only show A B
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