# [R] How to remove similar successive objects from a vector?

Gavin Simpson gavin.simpson at ucl.ac.uk
Wed Aug 16 13:21:23 CEST 2006

```On Wed, 2006-08-16 at 13:01 +0300, Atte Tenkanen wrote:
> Thanks for all respondents!
>
> I wasn't precise enough, when I enclosed my example. In fact, I need a
> version which works with all kinds of symbolic data, not only with
> numbers. So these versions
>
> rle(VECTOR)\$values
>
> and
>
> VECTOR=c(3,2,2,3,4,4,5,5,5,3,3,3,5,1,6,6)
> NEWVECTOR <- ifelse(VECTOR[-length(VECTOR)]==VECTOR[-1],NA,VECTOR)
> NEWVECTOR[!is.na(NEWVECTOR)]

Note that the above is not giving the same answer as
rle(VECTOR)\$values :

> VECTOR=c(3,2,2,3,4,4,5,5,5,3,3,3,5,1,6,6)
> NEWVECTOR <- ifelse(VECTOR[-length(VECTOR)]==VECTOR[-1],NA,VECTOR)
> NEWVECTOR[!is.na(NEWVECTOR)]
[1] 3 2 3 4 5 3 5 1
> rle(VECTOR)\$values
[1] 3 2 3 4 5 3 5 1 6
> all.equal(NEWVECTOR[!is.na(NEWVECTOR)], rle(VECTOR)\$values)
[1] "Numeric: lengths (8, 9) differ"

So make sure you use the rle solution.

G

>
>
> I made a test and the first version was 2.5x faster with my data, but
> both works enough fast.
>
> Atte
>
> On Wed, 2006-08-16 at 08:58 +0100, Patrick Burns wrote:
> > I think
> >
> > rle(VECTOR)\$values
> >
> > will get you what you want.
> >
> > Patrick Burns
> > patrick at burns-stat.com
> > +44 (0)20 8525 0696
> > http://www.burns-stat.com
> > (home of S Poetry and "A Guide for the Unwilling S User")
> >
> > Atte Tenkanen wrote:
> >
> > >Is there some (much) more efficient way to do this?
> > >
> > >VECTOR=c(3,2,4,5,5,3,3,5,1,6,6);
> > >NEWVECTOR=VECTOR[1];
> > >
> > >for(i in 1:(length(VECTOR)-1))
> > >{
> > >	if((identical(VECTOR[i], VECTOR[i+1]))==FALSE){
> > >		NEWVECTOR=c(NEWVECTOR,VECTOR[i+1])}
> > >}
> > >
> > >
> > >
> > >>VECTOR
> > >>
> > >>
> > > [1] 3 2 4 5 5 3 3 5 1 6 6
> > >
> > >
> > >>NEWVECTOR
> > >>
> > >>
> > >[1] 3 2 4 5 3 5 1 6
> > >
> > >_______________________________
> > >Atte Tenkanen
> > >University of Turku, Finland
> > >
> > >______________________________________________
> > >R-help at stat.math.ethz.ch mailing list
> > >https://stat.ethz.ch/mailman/listinfo/r-help
> > >and provide commented, minimal, self-contained, reproducible code.
> > >
> > >
> > >
> > >
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> and provide commented, minimal, self-contained, reproducible code.
--
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Gavin Simpson                 [t] +44 (0)20 7679 0522
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```