regexp quickie
Phil Carmody
wish to extract from that the 1 or 2 letters which are closest to the n-th
character in the string. Is there a simple regexp to perform that task?
e.g.
if the string=A_Z_K_ then:
if n=1, then I want 'A' (or 'AA', not fussed)
if n=2, then I want 'AZ'
if n=3, then I want 'Z' (or 'ZZ', not fussed)
if n=4, then I want 'ZK'
if n=5 or 6, then I want 'K' (or 'KK', not fussed)
I can see how to do it with the concatenation of two matches from two substrs,
but that's barely simpler than a naive loop over each character forwards and
backwards.
Phil
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Ronald J Kimball
> Say I had a string satisfying /^[A-Z_]{6}$/, but not equal to '______'
> and I wish to extract from that the 1 or 2 letters which are closest to
> the n-th character in the string. Is there a simple regexp to perform
> that task?
>
> e.g.
> if the string=A_Z_K_ then:
> if n=1, then I want 'A' (or 'AA', not fussed)
> if n=2, then I want 'AZ'
> if n=3, then I want 'Z' (or 'ZZ', not fussed)
> if n=4, then I want 'ZK'
> if n=5 or 6, then I want 'K' (or 'KK', not fussed)
>
> I can see how to do it with the concatenation of two matches from two
> substrs, but that's barely simpler than a naive loop over each character
> forwards and backwards.
Well, I wouldn't exactly call this regex simple... But I have come up with
one that does it:
for (qw/ A_Z_K_ A_____ _____K /) {
print "$_\n";
for my $n (1 .. 6) {
my $r = $n - 1;
print "$n: ";
/^(?(?=.{0,$r}[A-Z]).{0,$r}|.*)([A-Z])(?(?<!^..{$r}).*?([A-Z]|$))/
&& print "$1 $2";
print "\n";
}
}
This has the advantage of always putting the matched characters in $1 and
$2. (Note that $1 is always set; if there is no letter at or before the
position, $1 will contain the first letter after the position and $2 will
be empty.)
Here are two other approaches:
/^.{$r}([A-Z])/ || /^.{0,$r}([A-Z]).*?([A-Z]|$)/ || /^.*([A-Z])/
&& print "$1 $2";
is simpler, but uses three separate regular expressions.
/^.{$r}([A-Z])|^.{0,$r}([A-Z]).*?([A-Z]|$)|^.*([A-Z])/
&& print $1 || $4 || "$2 $3";
uses a single regular expression, but the results will be in $1, or in $2
and $3, or in $4. (And if digits were allowed the print logic would need
to be modified.)
Ronald
Phil Carmody
> On Wed, Jun 27, 2007 at 05:45:54AM -0700, Phil Carmody wrote:
> > Say I had a string satisfying /^[A-Z_]{6}$/, but not equal to '______'
> > and I wish to extract from that the 1 or 2 letters which are closest to
> > the n-th character in the string. Is there a simple regexp to perform
> > that task?
>
> one that does it:
> /^.{$r}([A-Z])/ || /^.{0,$r}([A-Z]).*?([A-Z]|$)/ || /^.*([A-Z])/
> /^.{$r}([A-Z])|^.{0,$r}([A-Z]).*?([A-Z]|$)|^.*([A-Z])/
Woh! I'm glad that's complicated, as I don't feel so bad just doing it the
naive way. (I chose the loop, rather than the joining of the result from two
substrs, one using a /^ match and the other using a $/.)
I have another idea how to solve the problem of isolating the (1 or) 2 closest
real letters:
In the A_Z_K_ case, for n=2 (r=1), an equally useful output could be
A_Z___
That is, to replace anything beyond the first letter at or after char r with
the underscore. Two passes would be necessary, one to strip that which is
before, one to strip that which is after.
Of course, I can probably simplify things by handling the cases of when there
is and is not a letter at the point of interest separately. If there is a
letter there, the answer is already found.
It's not a big deal, I was just noodling...
Thanks for the rather heroic regexps though!
Phil
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Roy Johnson
for (qw/ A_Z_K_ A_____ _____K /) {
print "$_\n";
for my $n (1 .. 6) {
my $r = $n - 1;
print "$n: ";
print /^(?=.{0,$r}([^_]))?.{0,$r}.*?([^_])/
? "[$1] ($2)" : "no match";
print "\n";
}
}
Ronald J Kimball
I wish I'd thought of doing it that way!
If you want $2 to only ever be the first letter at or after the target
location, you can just tweak the second half of the regex:
/^(?=.{0,$r}([^_]))?(?:.{$r}.*?([^_]))?/
Ronald
Roy Johnson
> location, you can just tweak the second half of the regex:
>
> /^(?=.{0,$r}([^_]))?(?:.{$r}.*?([^_]))?/
Save a stroke:
/^(?=.{0,$r}([^_]))?(?:.{$r,}?([^_]))?/
Roy
Phil Carmody
You guys amaze me! (And gals, too, in case Abigail reads this list. In which
case she might reduce that it is for RoRoRo's EinStein bot!)
Phil
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Shlomi Fish
> --- Roy.J...@shell.com wrote:
> > Mine (borrowing RJK's testing code): $1 will be the last letter
> > (non-underscore) before or at the target location; $2 will be the first
> > letter at or after the target location, or the last letter if no such
> > letter exists.
> >
> > for (qw/ A_Z_K_ A_____ _____K /) {
> > print "$_\n";
> > for my $n (1 .. 6) {
> > my $r = $n - 1;
> > print "$n: ";
> > print /^(?=.{0,$r}([^_]))?.{0,$r}.*?([^_])/
> > ? "[$1] ($2)" : "no match";
> > print "\n";
> > }
> > }
>
> You guys amaze me! (And gals, too, in case Abigail reads this list. In
> which case she might reduce that it is for RoRoRo's EinStein bot!)
>
Sorry to disappoint you but Abigail is a guy (at least in the context of
Perl):
{{{{{{{{{
Sep 18 22:11:57 <rindolf> fxn: Abigail is a guy, right?
Sep 18 22:12:23 <Yaakov> Abigail is a very Dutch, very male person.
Sep 18 22:12:35 <fxn> rindolf: yes
Sep 18 22:13:49 <rindolf> fxn: is Abigail his psedonym?
Sep 18 22:14:25 <fxn> rindolf: I don't know, his name in the conference was
Abigail
Sep 18 22:14:51 <fxn> rindolf: that's a picture by cog:
http://www.flickr.com/photos/cogurov/42641335/in/photostream/
Sep 18 22:14:52 <shorten> fxn's url is at http://xrl.us/hnmc
}}}}}}}}}
It is indeed a feminine name, though, at least in its Hebrew origin:
http://en.wikipedia.org/wiki/Abigail
Regards,
Shlomi Fish
> Phil
>
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>
> ___________________________________________________________________________
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--
---------------------------------------------------------------------
Shlomi Fish shl...@iglu.org.il
Homepage: http://www.shlomifish.org/
If it's not in my E-mail it doesn't happen. And if my E-mail is saying
one thing, and everything else says something else - E-mail will conquer.
-- An Israeli Linuxer
Phil Carmody
> On Thursday 28 June 2007, Phil Carmody wrote:
> > You guys amaze me! (And gals, too, in case Abigail reads this list.
>
> Perl):
> http://www.flickr.com/photos/cogurov/42641335/in/photostream/
Oh, that's going to get confusing... I'll have no idea what personal pronoun to
use when referring to hän in the future on littlegolem, usenet, and here.
Cop-out#1 - use of Finnish (genderless) pronouns.
Phil
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