[R] Regex engine types

[Gabor Grothendieck]

I get the same thing on "Version 2.3.1 Patched (2006-06-04 r38279)"
but on "R version 2.2.1, 2005-12-20" it gives character(0), as
expected, so there is some change between versions of R.  I am
on Windows XP.

On 6/9/06, Patrick Connolly <p_connolly at ihug.co.nz> wrote:
> > version
>         _
> platform x86_64-unknown-linux-gnu
> arch     x86_64
> os       linux-gnu
> system   x86_64, linux-gnu
> status
> major    2
> minor    2.1
> year     2005
> month    12
> day      20
> svn rev  36812
> language R
> >
>
> > grep("[W-Z]", LETTERS, value = TRUE)
> [1] "W" "X" "Y" "Z"
>
> That's what I'd have expected.
>
> > grep("[W-Z]", letters, value = TRUE)
> [1] "x" "y" "z"
>
> Not what I'd have thought.  However,
>
> > grep("[B-D]", letters, value = TRUE, perl = TRUE)
> character(0)
>
> So what is it that standard regular expressions use that's different
> from Perl-type ones?
>
> The help file for grep refers to POSIX 1003.2 which looked a bit
> daunting to delve into.  From my limited reading, it seems there are
> different gegex "Engine Types" which seems to be getting somewhat
> tangential to what I was working on.  I could probably avoid problems
> if I always set perl=TRUE, but it would be good to know what basic and
> extended regular expressions do that's different.  If someone has a
> quick line or two describing it, I'd be interested to know.
>
> Thanks
>
> --
> ~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.
>   ___    Patrick Connolly
>  {~._.~}                         Great minds discuss ideas
>  _( Y )_                        Middle minds discuss events
> (:_~*~_:)                        Small minds discuss people
>  (_)-(_)                                   ..... Anon
>
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>
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