http://qs321.pair.com?node_id=687755


in reply to Re^2: cleaving a sequence with specific alphabets
in thread cleaving a sequence with specific alphabets

You won't need capturing parentheses when evaluating in list context. Afaik does the .*? invoke a speed penalty, so that the expression might be optimized as:

     ...
     my @arr = $string =~ /
                      [^KR]+  # collect non K|R
                      .       # the following must be K|R
                      (?!P)   # ignore if fragment would start by P
                     /gsx;                
     ...

[download]

Regards

mwa

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Re^4: cleaving a sequence with specific alphabets
by tachyon-II (Chaplain) on May 21, 2008 at 16:30 UTC

    This is broken, not optimised. The .*? was there for a reason. 

    $string = "RYOURPOSTBROKEN";

    [download]
[reply]
[d/l]
      That snippet shows that yours is broken too. It doesn't return the last segment ("EN"). 
      my $string = "RYOURPOSTBROKEN";

print("input:     $string\n");
print("expecting: R YOURPOSTBR OK EN\n");
print("\n");

{  #  mwah (split)
   my $re = qr/(?<=[KR])(?!P)/;
   my @arr = split $re, $string;
   print("split $re: @arr\n");
}

{  # tachyon-II (re)
   my $re = qr/(.*?[KR])(?!P)/s;
   my @arr = $string =~ /$re/g;
   print("$re: @arr\n");
}

{  # mwah (re)
   my $re = qr/[^KR]+.(?!P)/s;
   my @arr = $string =~ /$re/g;
   print("$re: @arr\n");
}

      [download]
      input:     RYOURPOSTBROKEN
expecting: R YOURPOSTBR OK EN

split (?-xism:(?<=[KR])(?!P)): R YOURPOSTBR OK EN
(?s-xim:(.*?[KR])(?!P)): R YOURPOSTBR OK
(?s-xim:[^KR]+.(?!P)): YOU POSTBR OK EN
(?s-xim:[^KR]*.(?!P)): R YOU POSTBR OK EN

      [download]
[reply]
[d/l]
[select]

        Oh well, I made a mistake (better really test the code next time).

        I couldn't come up with a solution dropping the .*?, so Tachyon-II's solution only needs a slight modification ...

        ...
my @arr = $string =~ / .*? [KR] (?!P)  | [^KR]+$ /gx;
...

        [download]

        ... for getting the strings tail.

        Thanks for checking this!

        Regards

        mwa

[reply]
[d/l]

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