[R] strsplit("dia ma", "\\b") splits characterwise

[Joris Meys]

l guess this is expected behaviour, although counterintuitive. \b
represents an empty string indicating a word boundary, but is coerced
to character and thus simply the empty string. This means the output
you get is the same as
> strsplit("dia ma", "",perl=T)
[[1]]
[1] "d" "i" "a" " " "m" "a"

I'd use the seperating character as split in strsplit, eg

> strsplit("dia ma", "\\s")
[[1]]
[1] "dia" "ma"

If you need the space in the list as well, you'll have to go around it I guess.

> test <- as.vector(gregexpr("\\b", "dia ma", perl=TRUE)[[1]])
> test
[1] 1 4 5 7
> apply(embed(test,2),1,function(x) substr("dia ma",x[2],x[1]-1))
[1] "dia" " "   "ma"

It would be nice if special characters like \b would be recognized by
strsplit as well though.

Cheers
Joris

On Thu, Jul 8, 2010 at 10:15 AM, Suharto Anggono Suharto Anggono
<suharto_anggono at yahoo.com> wrote:
> \b is word boundary.
> But, unexpectedly, strsplit("dia ma", "\\b") splits character by character.
>
>> strsplit("dia ma", "\\b")
> [[1]]
> [1] "d" "i" "a" " " "m" "a"
>
>> strsplit("dia ma", "\\b", perl=TRUE)
> [[1]]
> [1] "d" "i" "a" " " "m" "a"
>
>
> How can that be?
>
> This is the output of 'gregexpr'.
>
>> gregexpr("\\b", "dia ma")
> [[1]]
> [1] 1 2 3 4 5 6
> attr(,"match.length")
> [1] 0 0 0 0 0 0
>
>> gregexpr("\\b", "dia ma", perl=TRUE)
> [[1]]
> [1] 1 4 5 7
> attr(,"match.length")
> [1] 0 0 0 0
>
>
> The output from gregexpr("\\b", "dia ma", perl=TRUE) is what I expect. I expect 'strsplit' to split at that points.
>
> This is in Windows. R was installed from binary.
>
>> sessionInfo()
> R version 2.11.1 (2010-05-31)
> i386-pc-mingw32
>
> locale:
> [1] LC_COLLATE=English_United States.1252
> [2] LC_CTYPE=English_United States.1252
> [3] LC_MONETARY=English_United States.1252
> [4] LC_NUMERIC=C
> [5] LC_TIME=English_United States.1252
>
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
>
>
>
> R 2.8.1 shows the same 'strsplit' behavior, but the behavior of default 'gregexpr' (i.e. perl=FALSE) is different.
>
>> strsplit("dia ma", "\\b")
> [[1]]
> [1] "d" "i" "a" " " "m" "a"
>
>> strsplit("dia ma", "\\b", perl=TRUE)
> [[1]]
> [1] "d" "i" "a" " " "m" "a"
>
>> gregexpr("\\b", "dia ma")
> [[1]]
> [1] 1 4 5 7
> attr(,"match.length")
> [1] 0 0 0 0
>
>> gregexpr("\\b", "dia ma", perl=TRUE)
> [[1]]
> [1] 1 4 5 7
> attr(,"match.length")
> [1] 0 0 0 0
>
>> sessionInfo()
> R version 2.8.1 (2008-12-22)
> i386-pc-mingw32
>
> locale:
> LC_COLLATE=English_United States.1252;LC_CTYPE=English_United States.1252;LC_MON
> ETARY=English_United States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252
>
>
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
>
>
>
>
> ______________________________________________
> 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.
>



-- 
Joris Meys
Statistical consultant

Ghent University
Faculty of Bioscience Engineering
Department of Applied mathematics, biometrics and process control

tel : +32 9 264 59 87
Joris.Meys at Ugent.be
-------------------------------
Disclaimer : http://helpdesk.ugent.be/e-maildisclaimer.php