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[Eloi Mercier]

There's no need for 'strsplit' here.

new=c("AAAABBBBBABBBABB")
A2B <- gregexpr("AB", new)
B2A <- gregexpr("BA", new)
length(A2B[[1]]) #3
length(B2A[[1]]) #2

Cheers,

Eloi

On 12-08-02 03:44 PM, David Winsemius wrote:
>
> On Aug 2, 2012, at 2:27 PM, rnewbie565 wrote:
>
>> I am trying to count the number of times that the characters in a string
>> change
>> For example-
>> new=c(AAAABBBBBABBBABB)
>
> Presumably you meant to quote that string.
>
>> I want to find the number of times that B changes to A and the number of
>> times that A changes to B. I tried the grep command but I only 
>> figured out
>> the positions of when B changes to A when I only need the number of 
>> times it
>> occurs.
>
> >  new=c('AAAABBBBBABBBABB')
> > unlist(strsplit(new,""))
>  [1] "A" "A" "A" "A" "B" "B" "B" "B" "B" "A" "B" "B" "B" "A" "B" "B"
> > rle(unlist(strsplit(new,"")))
> Run Length Encoding
>   lengths: int [1:6] 4 5 1 3 1 2
>   values : chr [1:6] "A" "B" "A" "B" "A" "B"
>
> > paste0( rle(unlist(strsplit(new,"")))$values, collapse="")
> [1] "ABABAB"
> > gregexpr("AB", .Last.value)
> [[1]]
> [1] 1 3 5
> attr(,"match.length")
> [1] 2 2 2
> attr(,"useBytes")
> [1] TRUE
>
>
> So the length of that list value could be used for the AB transitions. 
> Similarly for the BA ones
>
> > strrle <- paste0( rle(unlist(strsplit(new,"")))$values, collapse="")
> > length( gregexpr("BA", strrle)[[1]] )
> [1] 2
>
>>
>>
>>
>>
>> -- 
>> View this message in context: 
>> http://r.789695.n4.nabble.com/text-search-in-r-tp4638961.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.
>
> David Winsemius, MD
> Alameda, CA, USA
>
> ______________________________________________
> 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.
>
>


-- 
Eloi Mercier
Bioinformatics PhD Student, UBC
Paul Pavlidis Lab
2185 East Mall
University of British Columbia
Vancouver BC V6T1Z4