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

Probably not as good as the split solution but perhaps a little easier to read if you recognise the idiom: 

@arr = $string =~ m/(.*?[KR])(?!P)/gs;

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Re^3: cleaving a sequence with specific alphabets
by mwah (Hermit) on May 21, 2008 at 12:10 UTC

    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;                
     ...

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    Regards

    mwa

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[d/l]

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

      $string = "RYOURPOSTBROKEN";

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[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

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