[R] regular expression change in R version 2.3.0?

[Gabor Grothendieck]

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
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>
> E-mail: thomas.girke at ucr.edu
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>
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