Re: [Rd] duplicates() function

From: Duncan Murdoch <murdoch.duncan_at_gmail.com>
Date: Fri, 08 Apr 2011 11:15:47 -0400

On 08/04/2011 11:08 AM, Joshua Ulrich wrote:
> How about:
>
> y<- rep(NA,length(x))
> y[duplicated(x)]<- match(x[duplicated(x)] ,x)

That's a nice solution for vectors. Unfortunately for me, I have a matrix (which duplicated() handles by checking whole rows). So a better example that I should have posted would be

x <- cbind(1, c(9,7,9,3,7) )

and I'd still like the same output

> duplicated(x)

[1] FALSE FALSE TRUE FALSE TRUE
> duplicates(x)

[1] NA NA 1 NA 2

Duncan Murdoch

> --
> 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
> >
> > ______________________________________________
> > R-devel_at_r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
> >



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