If you have to evaluate the average for all sequences, you can build the following hash: 
my %occurrences;
push @{$occurrences{$sequence[$_]}}, $numbers[$_]
   foreach (0 .. $#sequence);

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At this point, each entry in the hash has a "sequence" for key and a reference to an array containing the "numbers" for that sequence as value - computing the average should be pretty easy, e.g.: 
my $sum;
$sum += $_ foreach (@{$occurrences{'atcg'}});
my $average = $sum / scalar(@{$occurrences{'atcg'}});

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I leave the union of the two snippets as an exercise, just in case it's an homework :)

Update: fixed a typo in first snipped, thanks to Postular Postulant.

Flavio (perl -e "print(scalar(reverse('ti.xittelop@oivalf')))")

Don't fool yourself.

In reply to Re: finding matches in the same array by polettix
in thread finding matches in the same array by Anonymous Monk

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