Why on earth would you want to do that?
You'd want to do that in perl if the original input contains duplicates and you only want to show unique license plate numbers. Since perl doesn't have a built-in concept of a (uniqe) set hashes are the natural structure to use.

To the OP: note that i use sort here, but that's just because I presume you'd want the output to be predictable. 

$plates{$lets}{$number} =1;  # or $plates{$lets}{$number}++ if you wan
+t to count
# and
for my $let (sort keys %plates) {
  print "$let ",join(", ",sort keys %{$plates{$let}}),"\n";
}

[download]
Updated: removed map() - code should now be correct
"What should it profit a man, if he should win a flame war, yet lose his cool?"

In reply to Re^2: hash of hashes by Joost
in thread hash of hashes by volcan

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