my %data;
my $csv = Text::CSV_XS->new();
scalar <$fh>;
while (my $row = $csv->getline($fh))
{
  $data{$row->[0]}{sum} += $row->[1];
  $data{$row->[0]}{count}++;
}

for my $weeknum (sort keys %data)
{
  printf "%s %d %.1f\n", $weeknum,
                         $data{$weeknum}{sum} / $data{$weeknum}{count},
                         $data{$weeknum}{count};
}