my $last_key = "";
my @last_error_rates;
while (my $line = <DATA>) {
  my ($key, $error_rate) = split /\s+/, $line;

  if ($key ne $last_key) {
    # We just crossed a key boundary, do processing.
    process_block($last_key, @last_error_rates) if $last_key;
    $last_key = $key;
    @last_error_rates = ();
  }

  push @last_error_rates, $error_rate
}

# Don't forget the final block!
process_block($last_key, @last_error_rates);