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
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
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
> http://www.R-project.org/posting-guide.html
>
Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm
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 > > ______________________________________________ > R-help at stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html >
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 <r.hankin at noc.soton.ac.uk> 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 > > ______________________________________________ > R-help at stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html >