Another route is to rethink your data structure; if you have an array of hashs w/ each hash having 2 sort/index fields, try a hash (w/ count as the key) where the values are arrays of hashs which have type, a_point, z_point, error as members, something like:

foreach $count ( sort keys %data ){
# there's a better notation for this but $data{$count}->@
# never works for my foreachs ;->
  foreach $type_hash ( @{ $data{$count} } ) {
    print "$count";
   # just to make it easier to see, loop through the keys
   # for the type hash in your order. NB type_hash is 
   # hash ref ($$type_hash)
    foreach $val ( (qw(type a_point z_point error) ) ) {
      print " --> $$type_hash{$val}";
    }           # foreach val
    print "\n";
  }             # foreach type_hash
}               # foreach count
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This may be way off, for your data - the thought is that if you're having to work this hard to sort your data structure, you should think about changing your struct. Assuming you have data like:

count|type|a point|z point|error
3    |bz  |6.0    |7.2    |none
3    |boz |2.0    |1.1    |off by one
5    |bz  |3.5    |2.2    |ugly

you could:

while(<DATA>) {
  chomp;
  my ($count, $type, $a_point, $z_point, $error) 
       = split(/\|/);
  push @{ $data{$count} }, {type => $type, 
                 a_point => $a_point, z_point => $z_point,
                 error => "$error",
                 };
}    # while DATA
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a