[R] how to concatenate factor vectors?

[Sam Steingold]

How do I concatenate two vectors of factors?
--8<---------------cut here---------------start------------->8---
> a <- factor(5:1,levels=1:9)
> b <- factor(9:1,levels=1:9)
> str(c(a,b))
 int [1:14] 5 4 3 2 1 9 8 7 6 5 ...
> str(unlist(list(a,b),use.names=FALSE))
 Factor w/ 9 levels "1","2","3","4",..: 5 4 3 2 1 9 8 7 6 5 ...
--8<---------------cut here---------------end--------------->8---
so, unlist(list()) works.
is there a better way or is this how this is supposed to be done?
Thanks!
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