Sorry for my long post. I now summarized my real problem in a small example.

#!/usr/bin/perl

use strict;
use warnings;

use Data::TreeDumper;

my $s = {'name' => 'Homer',
         'surname' => 'Simpson',
         'kids' => [ { 'name' => 'Bart',
                       'surname' => 'Simpson' },
                     { 'name' => 'Lisa',
                       'surname' => 'Simpson' },
                     { 'name' => 'Maggie',
                       'surname' => 'Simpson' }],
         'wife' => { 'name' => 'Marge',
                     'surname' => 'Simpson' }};


             
my $OnlyName = sub
{
    my $s = shift ;
    
    if('HASH' eq ref $s)
    {
        # TODO
        
         return('HASH', undef, grep { /^name$/} keys %$s) ;
    }
    
    return(Data::TreeDumper::DefaultNodesToDisplay($s)) ;
};

print DumpTree($s,
               'The Simpsons',
               DISPLAY_ADDRESS => 0,
               FILTER => $OnlyName) ;



############################################################
# UNFILTERED OUTPUT
############################################################

#The Simpsons
#|- kids 
#|    |- 0 
#|    |  |- name = Bart 
#|    |  `- surname = Simpson 
#|      |- 1 
#|      |  |- name = Lisa 
#|      |  `- surname = Simpson 
#|      `- 2 
#|         |- name = Maggie 
#|         `- surname = Simpson 
#|- name = Homer 
#|- surname = Simpson 
#`- wife 
#   |- name = Marge 
#   `- surname = Simpson 
 

############################################################
# FILTERED OUTPUT  (only name)
############################################################

#The Simpsons
#|- kids 
#|    |- 0 
#|    |  |- name = Bart 
#|      |- 1 
#|      |  |- name = Lisa  
#|      `- 2 
#|      |- name = Maggie  
#|- name = Homer 
#`- wife 
#   |- name = Marge

[download]

I have a hash. I want to print it with Data::TreeDumper. My goal is it to only print the keys of the hash which are called "name". (see FILTERED OUTPUT (only name)).

How do I have to write the filter? My suggestion was 

return('HASH', undef, grep { /^name$/} keys %$s) ;

[download]
but this is NOT working.

Thank you for your help.

In reply to Re^2: Help to understand the Data::TreeDumper Filters by Dirk80
in thread Help to understand the Data::TreeDumper Filters by Dirk80

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