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How to flatten hashes?

by hoppfrosch (Beadle)
on Jul 14, 2005 at 07:22 UTC ( #474783=perlquestion: print w/ replies, xml ) Need Help??
hoppfrosch has asked for the wisdom of the Perl Monks concerning the following question:

Hi all,

I'm looking for a simple way to "flatten" hashes.
For example I have a hash that looks like this: 
accesslevels' => {
  'function' => {
    'func1' =>   {
                   'content' => 'val1'
                 },
    'default' => {
                   'content' => 'val2'
                 }
  }
}

[download]
What's the easiest (most elegant) way to remove the 'function' and the 'content' so that I get something like: 
accesslevels' => {
  'func1' => 'val1'
  'default' => 'val2'
}

[download]

Thanks

Hoppfrosch

Comment on How to flatten hashes?
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Re: How to flatten hashes?
by dirac (Beadle) on Jul 14, 2005 at 08:03 UTC
    #!/usr/bin/perl -w
use strict;
use Data::Dumper;

my %a = ('accesslevels' => {
                  'function' =>  {
                         'func1' =>   {
                                             'content' => 'val1'
                                          },
                         'default' => {
                                             'content' => 'val2'
                                          }
                  }
            }
);


my %b = map { $_, 
                    { 
                      func1 =>
                      $a{$_}{function}{func1}{content} ,
                      default =>
                      $a{$_}{function}{default}{content}
                    } 
                } keys %a;


print Dumper(%a);
print Dumper(%b);

    [download]
    Update:
    This works for generic hash with the same structure.
    Try with ... 
    my %a = ('accesslevels' => {
                  'function' =>  {
                         'func1' =>   {
                                             'content' => 'val1'
                                          },
                         'default' => {
                                             'content' => 'val2'
                                          }
                  }
            } ,
            'accesslevels1' => {
                  'function' =>  {
                         'func1' =>   {
                                             'content' => 'val3'
                                          },
                         'default' => {
                                             'content' => 'val4'
                                          }
                  }
            } ,
            'accesslevels2' => {
                  'function' =>  {
                         'func1' =>   {
                                             'content' => 'val5'
                                          },
                         'default' => {
                                             'content' => 'val6'
                                          }
                  }
            } ,
            'accesslevels3' => {
                  'function' =>  {
                         'func1' =>   {
                                             'content' => 'val7'
                                          },
                         'default' => {
                                             'content' => 'val8'
                                          }
                  }
            } ,
            'accesslevels4' => {
                  'function' =>  {
                         'func1' =>   {
                                             'content' => 'val9'
                                          },
                         'default' => {
                                             'content' => 'val10'
                                          }
                  }
            } ,
            
);


    [download]
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Re: How to flatten hashes?
by rev_1318 (Chaplain) on Jul 14, 2005 at 08:09 UTC
    If your hash is all you show us, you can simply say:
    my %newhash = (
    accesslevels => {
        func1   => $oldhash{function}{func1}{content},
        default => $oldhash{function}{default}{content}
    }
);

    [download]
    But if it is more generic (which I'm guessing it is), a possible approach can be:
    my %newhash;
foreach my $key1 (keys %oldhash) {
    foreach my $key2 (keys %{$oldhash{$key1}}) {
        foreach my $key3 (keys %{$oldhash{$key1}{$key2}}) {
            $newhash{$key1}{$key3} = $oldhash{$key1}{$key2}{$key3}{con
+tent}
        }
    }
}

    [download]
    HTH

    Paul

[reply]
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Re: How to flatten hashes?
by duelafn (Priest) on Jul 14, 2005 at 12:01 UTC

    Not sure this qualifies as more elegant, or just more obfuscated than rev_1318's solution. 

    use YAML;

my %h = (
'accesslevels' => {
  'function' => {
    'func1'   => { 'content' => 'val1' },
    'default' => { 'content' => 'val2' }
  }
},
'accesslevels2' => {
  'function' => {
    'func1'   => { 'content' => 'val1' },
    'default' => { 'content' => 'val2' }
  }
});

for my $L (values %h) {
  my (%tmp, $k, $v);
  for (values %$L) {
    $tmp{$k} = $$v{content} while ($k,$v) = each %$_;
  }
  $L = \%tmp;
}

print Dump \%h;

    [download]

    Good Day,
        Dean

[reply]
[d/l]
Re: How to flatten hashes?
by tlm (Prior) on Jul 14, 2005 at 13:13 UTC

    FWIW, 

    use strict;
use warnings;

my %hash = (
            accesslevels => {
                             function => {
                                          func1 =>   {
                                                      content => 'val1
+'
                                                     },
                                          default => {
                                                      content => 'val2
+'
                                                     }
                                         }
                            }
           );

sub flatten {
  my $hash = shift;
  while ( my ( $k, $v ) = each %$hash ) {
    next unless ref $v eq 'HASH';
    flatten( $v );
    exists $v->{ $_ } and $hash->{ $k } = $v->{ $_ }
      for qw( function content )
  }
}

use Dumpvalue;

flatten( \%hash );
print Dumpvalue->new->dumpValue( \%hash );

__END__
'accesslevels' => HASH(0x814cad4)
   'default' => 'val2'
   'func1' => 'val1'

    [download]

    the lowliest monk

[reply]
[d/l]
Re: How to flatten hashes?
by EvanCarroll (Chaplain) on Jul 14, 2005 at 20:50 UTC
    Because you mentioned "easiest":

    EXAMPLE HASH:
    my %foo = ( asdf => { foo => 'jkl' }, bar => { foo => 'func' }, );

    TRANSFORMATION CODE:
    map { $foo{$_} = $foo{$_}->{'foo'} } keys %foo;

    Evan Carroll
    www.evancarroll.com
[reply]

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