[R] Finding "runs" of TRUE in binary vector

[Vadim Ogranovich]

Untested:

c(TRUE, b[-1] != b[-length(b)]) gives you the (logical) indexes of the
beginnings of the runs
c(b[-1] != b[-length(b)], TRUE) gives you the (logical) indexes of the
ends of the runs

> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Sean Davis
> Sent: Thursday, January 27, 2005 2:14 PM
> To: r-help
> Subject: [R] Finding "runs" of TRUE in binary vector
> 
> I have a binary vector and I want to find all "regions" of 
> that vector that are runs of TRUE (or FALSE).
> 
>  > a <- rnorm(10)
>  > b <- a<0.5
>  > b
>   [1]  TRUE  TRUE  TRUE FALSE  TRUE FALSE  TRUE  TRUE  TRUE  TRUE
> 
> My function would return something like a list:
> region[[1]] 1,3
> region[[2]] 5,5
> region[[3]] 7,10
> 
> Any ideas besides looping and setting start and ends directly?
> 
> Thanks,
> Sean
> 
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