Using a reconstructed version of what may be your original data (with some extra variety thrown in for the contents of the bottom-level array references), maybe something like this:

c:\@Work\Perl>perl -wMstrict -le
"use Data::Dump qw(dd);
 ;;
 my %data = (
   'A1' => {
     'val1' => [23], 'val2' => [42, 99], 'val3' => [15], 'val4' => [10
+],
     },
   'B1' => {
     'val1' => [13], 'val2' => [], 'val3' => [25], 'val4' => [11],
     },
   );
 dd \%data;
 ;;
 for my $top_key (sort keys %data) {
   print qq{'$top_key':};
   for my $sub_key (sort keys %{ $data{$top_key} }) {
     print qq{  '$sub_key': (@{ $data{$top_key}{$sub_key} })};
     }
   }
"
{
  A1 => { val1 => [23], val2 => [42, 99], val3 => [15], val4 => [10] }
+,
  B1 => { val1 => [13], val2 => [], val3 => [25], val4 => [11] },
}

'A1':
  'val1': (23)
  'val2': (42 99)
  'val3': (15)
  'val4': (10)
'B1':
  'val1': (13)
  'val2': ()
  'val3': (25)
  'val4': (11)
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Please also see perldsc.