I am not sure whether this is desirable but here is another way just
in case:
paste(setdiff(a, a[duplicated(a)]))
You could replace paste with as.character if you prefer or
could remove it entirely if you want the result as a factor.
On 2/22/06, Robin Hankin <[EMAIL PROTECTED]> wrote:
> Hi.
>
> I have a factor and I want to extract just those elements that appear
> exactly once.
> How to do this?
>
> Toy example follows.
>
> > a <- as.factor(c(rep("oak",5) ,rep("ash",1),rep("elm",1),rep
> ("beech",4)))
> > a
> [1] oak oak oak oak oak ash elm beech beech beech beech
> Levels: ash beech elm oak
> > table(a)
> a
> ash beech elm oak
> 1 4 1 5
> >
>
> So I would want "ash" and "elm", because there is only one ash and
> only one elm in my wood.
>
> My Best Effort:
>
>
> > names(table(a)[table(a)==1])
> [1] "ash" "elm"
> >
>
> This doesn't seem particularly elegant to me; there must be a better
> way!
>
> anyone?
>
>
>
>
> --
> Robin Hankin
> Uncertainty Analyst
> National Oceanography Centre, Southampton
> European Way, Southampton SO14 3ZH, UK
> tel 023-8059-7743
>
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