in reply to cleaving a sequence with specific alphabets

Its not entirely clear for me what you try to do.

...
my @s = split /
               (?<=[KR])  # split on K,R
               (?!P)      # but not if in front of a P
              /x, 'APADPKGSTIDRPDAARTLTVHKCEQTDTRGVKEGTRNEDPQAECKPVSDV
+EFTITKLNVD';

print join "\n", @s;
...

[download]

The above would be my first guess here.

Regards

mwa

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Re^2: cleaving a sequence with specific alphabets
by tachyon-II (Chaplain) on May 21, 2008 at 11:31 UTC

    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;

    [download]
[reply]
[d/l]

      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

[reply]
[d/l]

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

        $string = "RYOURPOSTBROKEN";

        [download]
[reply]
[d/l]

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