Cool, I just needed to do more thinking. I think I have it figured out...

How's this?

use strict;

my %dataset;

while (<>) {
   # $_ => Id, Loc, Value, Etime

   my ($id, $loc, $value, $etime) = split(/,/, $_);

   $dataset{$id}{$etime} = { "Value" => $value,
                             "Loc" => $loc,
                           };
}

foreach my $id (sort keys %dataset) {
   foreach my $etime ( map { $_->[0] } sort sort_loc map { [$_, $datas
+et{$id}{$_}{Loc}] } keys %{$dataset{$id}} ) { 
      my $loc = $dataset{$id}{$etime}{Loc};
      my $value = $dataset{$id}{$etime}{Value};

      printf(STDOUT "%2s, %6s, %.1f, %i\n", $id, $loc, $value, $etime)
+;
   }
}

sub sort_loc {
   my ($loc_a, $head_a) = $a->[1] =~ /S(\d+)H(\d)/;
   my ($loc_b, $head_b) = $b->[1] =~ /S(\d+)H(\d)/;

   if (($head_a <=> $head_b) == 0) {
      $loc_a <=> $loc_b;
   }
   else {
      $head_a <=> $head_b;
   }
}
[download]

Thanks again!
Ryan