I can't imagine doing this myself after so carefully constructing a hash to index my data, but, this will do what you want: 

foreach my $key ( keys %hash ) { 
  while ( my ( $subkey, $value ) = each %{ $hash{$key} } ) { 
    $hash{ $subkey }{ $key } = $value;
  }
  delete $hash{ $key };
}

[download]

But what about when there are multiple occurrences of keyB in the original hash? Or multiple subkeys in the subhashes? 

#!/usr/bin/perl
use strict;
use warnings;
use feature qw/ say /;
use Data::Dumper;

my %hash;
$hash{'keyA'}{'keyB'} = '1234';
$hash{'keyC'}{'keyB'} = '5678';

say Dumper \%hash;

foreach my $key ( keys %hash ) { 
  while ( my ( $subkey, $value ) = each %{ $hash{$key} } ) { 
    $hash{ $subkey }{ $key } = $value;
  }
  delete $hash{ $key };
}

say Dumper \%hash;

__END__

[download]
Output: 
$VAR1 = {
          'keyA' => {
                      'keyB' => '1234'
                    },
          'keyC' => {
                      'keyB' => '5678'
                    }
        };

$VAR1 = {
          'keyB' => {
                      'keyC' => '5678',
                      'keyA' => '1234'
                    }
        };

[download]
.... is that really what you want?

The way forward always starts with a minimal test.

In reply to Re: inverting keys in a 2-D Hash by 1nickt
in thread inverting keys in a 2-D Hash by melmoth

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