From josh.m.ulrich at gmail.com  Fri Apr  8 17:08:12 2011
From: josh.m.ulrich at gmail.com (Joshua Ulrich)
Date: Fri, 8 Apr 2011 10:08:12 -0500
Subject: [Rd] duplicates() function
In-Reply-To: <4D9F22BE.5000502@gmail.com>
References: <bug-14552-16@http.bugs.r-project.org/bugzilla3/>
	<20110408142610.88AEC970477@ix.urbanek.info>
	<B722DD6C-3B97-46EC-B369-8316F0F65D1F@cbs.dk>
	<4D9F22BE.5000502@gmail.com>
Message-ID: <BANLkTimQEeXMPCjWaHuQZ74t8d0A_9XeyQ@mail.gmail.com>

How about:

y <- rep(NA,length(x))
y[duplicated(x)] <- match(x[duplicated(x)] ,x)

--
Joshua Ulrich ?| ?FOSS Trading: www.fosstrading.com



On Fri, Apr 8, 2011 at 9:59 AM, Duncan Murdoch <murdoch.duncan at gmail.com> wrote:
> I need a function which is similar to duplicated(), but instead of returning
> TRUE/FALSE, returns indices of which element was duplicated. ?That is,
>
>> x <- c(9,7,9,3,7)
>> duplicated(x)
> [1] FALSE FALSE ?TRUE FALSE TRUE
>
>> duplicates(x)
> [1] NA NA ?1 NA ?2
>
> (so that I know that element 3 is a duplicate of element 1, and element 5 is
> a duplicate of element 2, whereas the others were not duplicated according
> to our definition.)
>
> Is there a simple way to write this function? ?I have ?an ugly
> implementation in R that loops over all the values; it would make more sense
> to redo it in C, if there isn't a simple implementation I missed.
>
> Duncan Murdoch
>
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>



[Rd] duplicates() function
Joshua Ulrich