R help - May 2004 - Finding indices where

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?

Thanks very much for any help/suggestions.
Ravi.

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