[R] elements that appear only once

[Dimitris Rizopoulos]

another approach is:

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

but I don't know if you find this more elegant :)


Best,
Dimitris

----
Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/(0)16/336899
Fax: +32/(0)16/337015
Web: http://www.med.kuleuven.be/biostat/
     http://www.student.kuleuven.be/~m0390867/dimitris.htm


----- Original Message ----- 
From: "Robin Hankin" <r.hankin at noc.soton.ac.uk>
To: "RHelp" <r-help at stat.math.ethz.ch>
Sent: Wednesday, February 22, 2006 10:11 AM
Subject: [R] elements that appear only once


> 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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