Serial Average

Just because I keep forgetting it and having to find out all the math manually again!

my $avg = 0;
my $cnt = 0;
for my $row (@rows) {
    if ($cnt) {
       $avg += (($row->{value} - $avg)/$cnt)*$row->{cnt};
       $cnt += $row->{cnt};
    } else {
       $cnt = $row->{cnt};
       $avg = $row->{value};
    }
}

Source: theMage