I get Can't use string ("1") as a HASH ref while "strict refs" in use. You seem to be hiding errors by not using use strict; use warnings;. no autovivification; would also be useful to you.

This kind of mistake elsewhere in your code would definitely explain your symptoms. You're placing all your data in one hash (%1), and you are linking to that hash throughout the tree.

I think your data structure is equivalent to the one below. It would also explain the infinite looping you are experiencing with the recursive solutions. 

%{"1"} = (
   cat2  => \%{"1"},
   cat21 => \%{"1"},
   cat22 => \%{"1"},
   cat3  => \%{"1"},
);

my %category = (
   cat1 => \%{"1"},
);

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In reply to Re^3: Printing a tree-view of a hash of hashes by ikegami
in thread Printing a tree-view of a hash of hashes by pdxperl

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