##
## Will process the records between $start and $end
## and count the occurances of the third
## field, returning the total count and a 
## has containing the individual counts keyed
## by the letter.  
##
sub processRec {
  my($arrayRef, $start, $end) = @_ ;
  my($i, $total, $letter_counts) ;
  my($position, $patient, $letter1, $letter2) ;
  
  for( $i = $start ; $i <= $end ; $i++ ) {
    ($position, $patient, $letter1, $letter2)=split(/\t/, $arrayRef->[$i]);

    $letter_counts->{uc $letter1} += 1 ;
  }
  $total = 0 ;
  for( values %$letter_counts ) {
    $total += $_ ;
  } # for

  return($total, $letter_counts) ;
}

@prettybase = map chomp, <INPUT> ;

#
# do something to determine start and stop points
#
($total, $counts) = processRec(\@prettybase, start, end) ;

while( ($letter, $count) = each %$counts ) {
  print "$letter => ", ($count*100)/$total, "\n" ;
}