[R] elements that appear only once

From: Robin Hankin <r.hankin_at_noc.soton.ac.uk>
Date: Wed 22 Feb 2006 - 20:11:51 EST


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@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
Received on Wed Feb 22 20:16:18 2006

This archive was generated by hypermail 2.1.8 : Fri 03 Mar 2006 - 03:42:39 EST