in reply to Printing a tree-view of a hash of hashes

Your specification is rather sparse. However a big heads up in your code is that you are using nested loops. That just ain't going to work. Every time you add a level to your hash you will need to add another nested loop and you really don't want to go there.

The common technique is to write a recursive sub to do the work. Consider:

use strict;
use warnings;
use 5.010;

my %categories = (
    level1 => {
        'level1-1' => {},
        'level1-2' => {'level1-2-1' => {}},
        'level1-3' => {},
        },
    level2 => {'level2-1' => {}},
    );

dumpHash(\%categories);

sub dumpHash {
    my ($subHash, $indent) = @_;

    $indent //= '';

    given (ref $subHash) {
        when ('') {print "$indent$subHash\n" if defined $subHash}
        when ('HASH') {
            for my $key (sort keys %$subHash) {
                print "$indent$key\n";
                dumpHash($subHash->{$key}, "$indent   ");
            }
        }
    }
}

[download]

Prints:

level1
   level1-1
   level1-2
      level1-2-1
   level1-3
level2
   level2-1

[download]
True laziness is hard work

Replies are listed 'Best First'.
Re^2: Printing a tree-view of a hash of hashes
by pdxperl (Sexton) on Jun 01, 2010 at 03:24 UTC
    Thanks -- btw, this works correctly! The other recursive example goes into an infinite loop. I'm not sure why, but at least I'm over one roadblock.
[reply]

      The other recursive example goes into an infinite loop.

      I presume you mean mine. If so, no it doesn't: 

      use strict;
use warnings;

sub print_tree {
   my ($tree, $depth) = @_;
   $depth ||= 0;
   my $indent = '...' x $depth;
   for (sort keys %$tree) {
      print($indent, /^\s*\z/ ? "<blank>" : $_, "\n");
      print_tree($tree->{$_}, $depth+1);
   }      
}

my %categories = (
    level1 => {
        'level1-1' => {},
        'level1-2' => {'level1-2-1' => {}},
        'level1-3' => {},
        },
    level2 => {'level2-1' => {}},
    );


print_tree(\%categories);

      [download]
      level1
...level1-1
...level1-2
......level1-2-1
...level1-3
level2
...level2-1

      [download]

      Unless, of course, you don't actually a have tree. Like I said before, %categories doesn't contain what you think it does.

[reply]
[d/l]
[select]
        Thanks -- I didn't mean that comment negatively, as I appreciate the help. Your example is fine with your data, but with mine it did appear to go into infinite recursion. And I agree, there is something odd with what's in the hash, but what I didn't understand was why was is OK in Data::Dumper? So I did track down the cause,which is boiled down to the testcase below. This is what strict was complaining about as the string ref error. I fixed the issue, however, I'm not sure why it causes the tree to be displayed so differently for my approach versus yours versus data dumper. I commented strict out so you can see how the display differs, I know strict normally shouldn't be commented out. Also, this is deliberately showing an error - I'm just showing the odd output that results from that error. 
        #use strict;
use Data::Dumper;

my %h;
$h{'B'}{1}=1; # this is the error which causes the display 
              # issues
for my $a ('A'..'C'){
   for my $b (0..2){
     for my $c ('a'..'c') {
        $h{$a}{$b}{$c}=1; # error if $h{$a}{$b} exists
     }
   }
}
print "Data Dumper-------------------\n";
print Dumper (\%h);
print "Loop----------------\n";
foreach my $top ( sort keys %h){
    if($top =~ /^\s*$/){$top="<blank>";}
    print "$top\n";
    foreach my $second ( sort keys %{$h{$top}}){
       if($second  =~ /^\s*$/){$second="<blank>";}
       print "...$second\n";
       foreach my $third (sort keys %{$h{$top}{$second}}){
        if($third  =~ /^\s*$/){$third="<blank>";}
           print "......$third\n";
       }
    }
}
print "Print_tree------------------\n";
print_tree(\%h);

sub print_tree {
   my ($tree, $depth) = @_;
   if($depth > 5) {
       print "max depth reached\n";
       return;
   }
   $depth ||= 0;
   my $indent = '...' x $depth;
   for (sort keys %$tree) {
      print($indent, /^\s*\z/ ? "<blank>" : $_, "\n");
      print_tree($tree->{$_}, $depth+1);
   }      
}

        [download]
[reply]
[d/l]

In Section Seekers of Perl Wisdom