Um... every time I run the program I get a different output. Is there some reason for the random number generator??

As far as coding style, there are no validity checks. If I feed garbage into the subroutine, it quietly gives me garbage out.

my %index_val = ( F => -1.8, O => 3, O => 4,
                  B => 'quxx', A => 2, R => 1,
                P=>'foo');
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$VAR1 = [
          {
            'A' => '2.25'
          },
          {
            'C' => '0.5'
          },
          {
            'T' => '0.5'
          },
          {
            'G' => '0.5'
          },
          {
            'A' => '2.25'
          },
          {
            'C' => '0.324074074074074'
          },
          {
            'N' => '0.324074074074074'
          }
        ];
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Update: I don't mind if a program fails on garbage input, but it should fail noisily.