What, dear monks, is the most efficient way of getting these arrays:

my @x_values_for_points_above_the_trend_line;
my @y_values_for_points_above_the_trend_line;
my @distances_above_the_trend_line;

my @x_values_for_points_below_the_trend_line;
my @y_values_for_points_below_the_trend_line;
my @distances_below_the_trend_line;

my @x_values_for_points_on_the_trend_line;
my @y_values_for_points_on_the_trend_line;

# The contents of these arrays have corresponding values in the same a
+rray positions.
[download]

... into a lookup hash so that I can perform operations like the following:

my $count_A = -1;
my @regions_A_array;


foreach (@x_values_for_points_above_the_trend_line) {
  
  $count_A++;

  my $x_value_SM = $_;
  my $y_value_SM = $y_values_for_points_above_the_trend_line[$count_A]
+;
  
  my $Select_area_above_trendline = "
     SELECT DISTINCT A.Region FROM Temp_table_A A, Temp_table_B B WHER
+E A.Region = B.Region AND A.SM = ".$x_value_SM." AND B.SM = ".$y_valu
+e_SM." 
  ";
  
  
  my $sth_atl = $dbh->prepare($Select_area_above_trendline) or die "Co
+uldn't prepare query: ".$dbh->errstr;
  $sth_atl->execute() or die "Couldn't execute query: ".$sth_atl->errs
+tr;
  
  my @regions_A;


  while (@regions_A = $sth_atl->fetchrow_array) {    
    push (@regions_A_array, @regions_A);    
  }

  my @regions_A_array = r(@regions_A_array);   #  This is to remove du
+plicates from the array
}



#  The subroutine below removes duplicates

sub r{
  keys%{{map{$_,1}@_}}
}
[download]

...... with the added functionality of printing out each region in the array @regions_A_array with the $distances_below_the_trend_line[$pos] value.


By the way, I accept that it looks like this process has been badly designed. It is an evolved piece of code.