R help - May 2006 - regular expression change in R version 2.3.0?

The interpretation of regular expressions with repetition
quantifiers in the 'gregexpr' function seems to have changed 
between R Version 2.2.0 and 2.3.0. The 'gsub' function, however, 
gives the same results in R Versions 2.2.0 and 2.3.0. Below is 
an example that demonstrates the version differences of the 
'gregexpr' function. I am not sure whether this new behavior 
is an intended change or represents a bug. Personally, I liked
the old behavior of this function more useful, since it is 
consistent with the Perl regular expressions.

Here are my questions:
(1) Is there a possibility to obtain from 'gregexpr' 
the old output of R version 2.2.0 when using regular 
expressions with repetition quantifiers.

(2) How can one be informed about regular expression changes 
and the associated functions in new versions of R? 


Here is the example code to demonstrate the version difference 
of the 'gregexpr' function between versions 2.3.0 and 2.2.0:

# Example string
x <- "xaaaaxaaaax"

# gregexpr in Version 2.2.0  (2005-10-06 r35749)
gregexpr("[a]{1,}", as.character(x), perl=T)
[[1]]
[1] 2 7
attr(,"match.length")
[1] 4 4

# gregexpr in Version 2.3.0 (2006-04-24)
gregexpr("[a]{1,}", as.character(x), perl=T)
[[1]]
[1]  2  3  4  5  7  8  9 10
attr(,"match.length")
[1] 4 3 2 1 4 3 2 1

# gsub gives expected output in Versions 2.2.0 & 2.3.0
gsub("[a]{1,}", "_", as.character(x), perl=T)
[1] "x_x_x"


Thanks in advance for your help.

Thomas

-- 
Thomas Girke, Ph.D.
1008 Noel T. Keen Hall
Center for Plant Cell Biology (CEPCEB)
University of California
Riverside, CA 92521

E-mail: thomas.girke at ucr.edu
Ph: 951-827-2469
Fax: 951-827-4437

If you need a workaround this works the same in R 2.2.1 and R 2.3.0 patched:

x <- "xaaaaxaaaax"
gregexpr("[^a]a+", paste("", x))


On 5/6/06, Thomas Girke <thomas.girke at ucr.edu>
wrote:
> The interpretation of regular expressions with repetition
> quantifiers in the 'gregexpr' function seems to have changed
> between R Version 2.2.0 and 2.3.0. The 'gsub' function, however,
> gives the same results in R Versions 2.2.0 and 2.3.0. Below is
> an example that demonstrates the version differences of the
> 'gregexpr' function. I am not sure whether this new behavior
> is an intended change or represents a bug. Personally, I liked
> the old behavior of this function more useful, since it is
> consistent with the Perl regular expressions.
>
> Here are my questions:
> (1) Is there a possibility to obtain from 'gregexpr'
> the old output of R version 2.2.0 when using regular
> expressions with repetition quantifiers.
>
> (2) How can one be informed about regular expression changes
> and the associated functions in new versions of R?
>
>
> Here is the example code to demonstrate the version difference
> of the 'gregexpr' function between versions 2.3.0 and 2.2.0:
>
> # Example string
> x <- "xaaaaxaaaax"
>
> # gregexpr in Version 2.2.0  (2005-10-06 r35749)
> gregexpr("[a]{1,}", as.character(x), perl=T)
> [[1]]
> [1] 2 7
> attr(,"match.length")
> [1] 4 4
>
> # gregexpr in Version 2.3.0 (2006-04-24)
> gregexpr("[a]{1,}", as.character(x), perl=T)
> [[1]]
> [1]  2  3  4  5  7  8  9 10
> attr(,"match.length")
> [1] 4 3 2 1 4 3 2 1
>
> # gsub gives expected output in Versions 2.2.0 & 2.3.0
> gsub("[a]{1,}", "_", as.character(x), perl=T)
> [1] "x_x_x"
>
>
> Thanks in advance for your help.
>
> Thomas
>
> --
> Thomas Girke, Ph.D.
> 1008 Noel T. Keen Hall
> Center for Plant Cell Biology (CEPCEB)
> University of California
> Riverside, CA 92521
>
> E-mail: thomas.girke at ucr.edu
> Ph: 951-827-2469
> Fax: 951-827-4437
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html
>

Hi,
  This has been reverted in R-devel, so you should get the old behavior
in it. Gabor Grothendieck posted a work around for R 2.3.x.

best wishes
   Robert


Thomas Girke wrote:
> The interpretation of regular expressions with repetition
> quantifiers in the 'gregexpr' function seems to have changed 
> between R Version 2.2.0 and 2.3.0. The 'gsub' function, however, 
> gives the same results in R Versions 2.2.0 and 2.3.0. Below is 
> an example that demonstrates the version differences of the 
> 'gregexpr' function. I am not sure whether this new behavior 
> is an intended change or represents a bug. Personally, I liked
> the old behavior of this function more useful, since it is 
> consistent with the Perl regular expressions.
> 
> Here are my questions:
> (1) Is there a possibility to obtain from 'gregexpr' 
> the old output of R version 2.2.0 when using regular 
> expressions with repetition quantifiers.
> 
> (2) How can one be informed about regular expression changes 
> and the associated functions in new versions of R? 
> 
> 
> Here is the example code to demonstrate the version difference 
> of the 'gregexpr' function between versions 2.3.0 and 2.2.0:
> 
> # Example string
> x <- "xaaaaxaaaax"
> 
> # gregexpr in Version 2.2.0  (2005-10-06 r35749)
> gregexpr("[a]{1,}", as.character(x), perl=T)
> [[1]]
> [1] 2 7
> attr(,"match.length")
> [1] 4 4
> 
> # gregexpr in Version 2.3.0 (2006-04-24)
> gregexpr("[a]{1,}", as.character(x), perl=T)
> [[1]]
> [1]  2  3  4  5  7  8  9 10
> attr(,"match.length")
> [1] 4 3 2 1 4 3 2 1
> 
> # gsub gives expected output in Versions 2.2.0 & 2.3.0
> gsub("[a]{1,}", "_", as.character(x), perl=T)
> [1] "x_x_x"
> 
> 
> Thanks in advance for your help.
> 
> Thomas
> 
-- 
Robert Gentleman, PhD
Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N, M2-B876
PO Box 19024
Seattle, Washington 98109-1024
206-667-7700
rgentlem at fhcrc.org