# hash to hold highest values
my %col6=();

while (my $line = <$data>) {
  chomp $line;
  my @fields = split "," , $line, -1;
  my $key = $fields[1].$fields[2];
  
  # store max values
  if ( $fields[5] > $col6{$key} ){
    $col6{$key} = $fields[5];
  }  
}

# reset to start
seek $data,0,0;

# read file 2nd time
while (my $line = <$data>) {
  chomp $line;
  my @fields = split "," , $line, -1;
  my $key = $fields[1].$fields[2];
  
  # reject lowest duplicate
  if ( $fields[5] < $col6{$key} ){
    # extra text added for debugging
	print OUTFILE_1 $line." - duplicate $key $col6{$key}\n"; 
  } else {
    print OUTFILE $line."\n";
  }
}