Hi Sam,

Perhaps the following?

> a <- factor(5:1,levels=1:9)
> b <- factor(9:1,levels=1:9)
> lev <- sort(unique(f <- c(a, b)))
> f <- factor(f, levels = lev)
> str(f)
 Factor w/ 9 levels "1","2","3","4",..: 5 4 3 2 1 9 8 7 6 5 ...

HTH,
Jorge.-


On Thu, Oct 18, 2012 at 3:44 PM, Sam Steingold <> wrote:

> 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!
> --
> Sam Steingold (http://sds.podval.org/) on Ubuntu 12.04 (precise) X
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