[R] matching a sequence in a vector?

[Gabor Grothendieck]

On Tue, Feb 14, 2012 at 11:17 PM, Redding, Matthew
<Matthew.Redding at deedi.qld.gov.au> wrote:
> I've been trawling through the documentation and listserv archives on this topic -- but
> as yet have not found a solution.  I'm sure this is pretty simple with R, but I cannot work out how without
> resorting to ugly nested loops.
>
> As far as I can tell, grep, match, and %in% are not the correct tools.
>
> Question:
> given these vectors --
> patrn <- c(1,2,3,4)
> exmpl <- c(3,3,4,2,3,1,2,3,4,8,8,23,1,2,3,4,4,34,4,3,2,1,1,2,3,4)
>
> how do I get the desired answer by finding the occurence of the pattern and returning the starting indices:
> 6, 13, 23
>

Here is a one-liner:

library(zoo)
which(rollapply(exmpl, 4, identical, patrn, fill = FALSE, align = "left"))

-- 
Statistics & Software Consulting
GKX Group, GKX Associates Inc.
tel: 1-877-GKX-GROUP
email: ggrothendieck at gmail.com