R help - Jun 2009 - find a sequence of characters in a vector

Hello,

I'm just looking for an easy way to find the positions of a complete
sequence in a bigger vector.
For example :
c("a","z","e") in
c("a","z","e","r","t","a","z","a","z","e","c")
and the result should be
1 8
that is the positions of the beginning of the complete sequence.

I tried with %in%, match, is.element but all I get is, for example
which(c("a","z","e") in
c("a","z","e","r","t","a","z","a","z","e","c"))
1 2 3
meaning that each character is in the bigger vector.

It must be easy, except for me. Sorry.

If you have a solution, thanks in advance to share it.
Have a good week-end,
Ptit Bleu.

-- 
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use gregexpr and paste
> aze <- paste(c("a", "z", "e"), collapse =
"")
> sequence <-
paste(c("a","z","e","r","t","a","z","a","z","e","c"),
collapse = "")
> gregexpr(aze, sequence, fixed = TRUE)
[[1]]
[1] 1 8
attr(,"match.length")
[1] 3 3

HTH,

--sundar

On Fri, Jun 5, 2009 at 6:22 AM, Ptit_Bleu<ptit_bleu at yahoo.fr>
wrote:
>
> Hello,
>
> I'm just looking for an easy way to find the positions of a complete
> sequence in a bigger vector.
> For example :
> c("a","z","e") in
c("a","z","e","r","t","a","z","a","z","e","c")
> and the result should be
> 1 8
> that is the positions of the beginning of the complete sequence.
>
> I tried with %in%, match, is.element but all I get is, for example
> which(c("a","z","e") in
c("a","z","e","r","t","a","z","a","z","e","c"))
> 1 2 3
> meaning that each character is in the bigger vector.
>
> It must be easy, except for me. Sorry.
>
> If you have a solution, thanks in advance to share it.
> Have a good week-end,
> Ptit Bleu.
>
> --
> View this message in context:
http://www.nabble.com/find-a-sequence-of-characters-in-a-vector-tp23888063p23888063.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

Here is one approach (this could be wrapped into a function if you are applying
it repeatedly):
> one <- c("a","z","e")
> two <-
c("a","z","e","r","t","a","z","a","z","e","c")
> 
> which( sapply( 1:(length(two)-length(one)+1), 
+ function(i) isTRUE( all.equal( one, two[ i + 0:(length(one)-1) ] ) ) ) )
[1] 1 8
>
Hope this helps,

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Ptit_Bleu
> Sent: Friday, June 05, 2009 7:22 AM
> To: r-help at r-project.org
> Subject: [R] find a sequence of characters in a vector
> 
> 
> Hello,
> 
> I'm just looking for an easy way to find the positions of a complete
> sequence in a bigger vector.
> For example :
> c("a","z","e") in
c("a","z","e","r","t","a","z","a","z","e","c")
> and the result should be
> 1 8
> that is the positions of the beginning of the complete sequence.
> 
> I tried with %in%, match, is.element but all I get is, for example
> which(c("a","z","e") in
c("a","z","e","r","t","a","z","a","z","e","c"))
> 1 2 3
> meaning that each character is in the bigger vector.
> 
> It must be easy, except for me. Sorry.
> 
> If you have a solution, thanks in advance to share it.
> Have a good week-end,
> Ptit Bleu.
> 
> --
> View this message in context: http://www.nabble.com/find-a-sequence-of-
> characters-in-a-vector-tp23888063p23888063.html
> Sent from the R help mailing list archive at Nabble.com.
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-
> guide.html
> and provide commented, minimal, self-contained, reproducible code.