Here is another solution that is a bit more flexible

tmp <- seq(8)
# split into your desired groups
max.groups <- 2
tmp.g <- split(tmp, ceiling(seq_along(tmp)/max.groups))

# do repeats, unlist, numeric index
as.numeric(unlist(rep(tmp.g, each = 2)))

Hope this works for you,
Charles


On Mon, Nov 11, 2013 at 10:16 AM, Carl Witthoft <carl@witthoft.com> wrote:

> Here's a rather extreme solution:
>
>  foo<-rep(1:6,each=2)
> Rgames> foo
>  [1] 1 1 2 2 3 3 4 4 5 5 6 6
>
> Rgames> foo[rep(c(1,3,2,4),3)+rep(c(0,4,8),each=4)]
>  [1] 1 2 1 2 3 4 3 4 5 6 5 6
>
> In the general case, then, it would be something like
>
> foo<- rep(1:N, each = 2)  # foo is of length(2*N)
>
> foo[rep(c(1,3,2,4),2*N/4 + rep( seq(0, 3*N/4,by=4),each=4)]
>
> Note that the refolding requires the sequence to have length a multiple of
> 4.
>
>
>
>
> Patrick Burns wrote
> >> f1
> > function(x) {
> >      one <- matrix(1:x, nrow=2)
> >      as.vector(rbind(one, one))
> > }
> > <environment: 0x000000000daaf1c0>
> >  > f1(8)
> >   [1] 1 2 1 2 3 4 3 4 5 6 5 6 7 8 7 8
> >
> > Pat
> >
> >
> > On 11/11/2013 12:11, Federico Calboli wrote:
> >> Hi All,
> >>
> >> I am trying to create an index that returns something like
> >>
> >> 1,2,1,2,3,4,3,4,5,6,5,6,7,8,7,8
> >>
> >> and so on and so forth until a predetermined value (which is obviously
> >> even).  I am trying very hard to avoid for loops or for loops front
> ends.
> >>
> >> I'd be obliged if anybody could offer a suggestion.
> >>
> >> BW
> >>
> >> F
> >>
> >>
> >>
> >> ______________________________________________
> >>
>
> > R-help@
>
> >  mailing list
> >> https://stat.ethz.ch/mailman/listinfo/r-help
> >> PLEASE do read the posting guide
> >> http://www.R-project.org/posting-guide.html
> >> and provide commented, minimal, self-contained, reproducible code.
> >>
> >
> > --
> > Patrick Burns
>
> > pburns@.seanet
>
> > twitter: @burnsstat @portfolioprobe
> > http://www.portfolioprobe.com/blog
> > http://www.burns-stat.com
> > (home of:
> >   'Impatient R'
> >   'The R Inferno'
> >   'Tao Te Programming')
> >
> > ______________________________________________
>
> > R-help@
>
> >  mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> > http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
>
>
>
>
>
> --
> View this message in context:
> http://r.789695.n4.nabble.com/repeating-values-in-an-index-two-by-two-tp4680210p4680234.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>



-- 
Charles Determan
Integrated Biosciences PhD Candidate
University of Minnesota

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