[R] Finding indices where

[Petr Pikal]

On 19 May 2004 at 13:26, Ravi Varadhan wrote:

> Hi:
> 
> Suppose I have the following vector:
> 
> > x <- c(1,4:8,11,13:14,17,19,23:28,35:38)
> > x
>  [1]  1  4  5  6  7  8  11 13 14 17 19 23 24 25 26 27 28 35 36 37 38 >
> 
> 
> and I would like to pick out the first and last indices of all the
> consecutive "runs" of integers, where the length of a run is no
> smaller than a specified value, say, nmin.  That is, in the above
> example, for nmin=4, I would like to get the following 3 by 2 matrix:
> 
> 4 8
> 23 28
> 35 38
> 
> For nmin=5, I would get the following 2 by 2 matrix
> 
> 4 8
> 23 28
> 
> and for nmin=6, I would get the following 1 by 2 matrix
> 
> 23 28
> 
> Is there an efficient and elegant way to do this?

Hallo
not complete maybe not ellegant but

y<-rle(diff(x))
res1<-x[(cumsum(y$length))[y$length>1]]+1
res2<-res1-y$length[y$length>1]

gives you the numbers you want in two vectors (res1,  res2). Than you can do 
any formating and selection you want.

Cheers
Petr

> 
> Thanks very much for any help/suggestions.
> Ravi.
> 
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Petr Pikal
petr.pikal at precheza.cz