R help - Apr 2008 - Consecutive zeros in a vector

Suppose X is a long vector of integers (typically about 30000 elements). Is
there an efficient way to detect whether there are at least N consecutive
zeros in X, and if yes, where does this occur?

for example, suppose X is:
  1 2 3 4 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 4 2 0 1 2 0 0 0 2 2 2 2 2 ...

and N is 10. I would like a foo(X, 10) to return something like c(6,19)
(start and end positions in X of at least 10 consecutive zeros). I can think
of a number of slow and probably inefficient ways of doing it (nested
loops..), but perhaps someone has a better idea..

Thanks in advance,
Kenn

	[[alternative HTML version deleted]]

On 29/04/2008 11:39 AM, Kenn Konstabel wrote:
> Suppose X is a long vector of integers (typically about 30000 elements). Is
> there an efficient way to detect whether there are at least N consecutive
> zeros in X, and if yes, where does this occur?
> 
> for example, suppose X is:
>    ...
> 
> and N is 10. I would like a foo(X, 10) to return something like c(6,19)
> (start and end positions in X of at least 10 consecutive zeros). I can
think
> of a number of slow and probably inefficient ways of doing it (nested
> loops..), but perhaps someone has a better idea..
Something based on rle() should be fairly easy.  rle(x)$lengths > 9 
identifies the long runs, cumsum(rle(x)$lengths) identifies where runs end.

Duncan Murdoch