[R] How to get duplicated items in a vector?

[William Dunlap]

Bill Dunlap
TIBCO Software Inc - Spotfire Division
wdunlap tibco.com  

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Peng Yu
> Sent: Thursday, October 01, 2009 7:42 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] How to get duplicated items in a vector?
> 
> Hi,
> 
> > x=c(rep(1,3),rep(3,2))
> > x
> [1] 1 1 1 3 3
> > duplicated(x)
> [1] FALSE  TRUE  TRUE FALSE  TRUE
> >
> 
> As shown in the above code, 'duplicated' doesn't return 'F' for the
> first '1' and first '3' in 'x'. I am wondering if there is a function
> that can return an indicator for any element whether it appears in a
> vector twice or more.

You could use is.element() or %in%, as in
   > x <- rep(3:1, 3:1)
   > x %in% x[duplicated(x)]
   [1]  TRUE  TRUE  TRUE  TRUE  TRUE FALSE

Bill Dunlap
TIBCO Software Inc - Spotfire Division
wdunlap tibco.com 

> 
> Regards,
> Peng
> 
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