[R] elements that appear only once

[Adaikalavan Ramasamy]

A slight variation on your solution but hopefully more readable:

	names( which( table(a) == 1 ) )

Regards, Adai



On Wed, 2006-02-22 at 09:11 +0000, Robin Hankin 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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