That is a great problem i.e. I found it a lot more difficult than it first appeared. I'm not sure I'd call this solution elegant, although it would look better if the code is cleaned up (a lot). I'd clean it up myself, but it's taken me most of this afternoon to work this out and the boss will have my hide if he finds out how little I've produced today. 
#!/usr/bin/perl -w
use strict;
use Dumpvalue;

# example structure
my $struct = { fruit => [qw( apple pear )],
               type => [qw( organic farmed )],
               period => { 20050824 => { to        => [ 'new york', 'l
+ondon', ],
                                         transport => 'air' },
                           20050825 => { to => 'auckland', },
                         } ,
               name   => 'bangers',
            };




#logHere $struct;
print "Input:\n";
Dumpvalue->new->dumpValue(  $struct ) ;

my $expanded = expand($struct, []);

print '='x80,"\nResult:\n";
Dumpvalue->new->dumpValue( $expanded ) ;

sub expand {
  my ( $struct, $expanded, $parent_key) =@_;
  for my $key ( sort keys %$struct ) {
    if ( ref($struct->{$key}) eq 'ARRAY' ) {
      if ( scalar @$expanded ) {
        $expanded = [ map { my $row = $_; map { my $newrow = {%$row}; 
+$newrow->{$key} = $_; $newrow }  @{$struct->{$key}} } @$expanded ];
      }
      else {
        push @$expanded,  map { { $key=> $_ } } @{$struct->{$key}} ;
      }
    }
    elsif ( ref $struct->{$key} eq 'HASH' ) {
      $parent_key ||='';
      my $expansion = expand($struct->{$key}, [], $key);
      $expansion  = [map { {%$_, $parent_key => $key}  } @$expansion] 
+if $parent_key;
      if ( scalar @$expanded ) {
        my $count = scalar @$expanded;
        $expanded = [ map { my $row = $_;
                            map { my $newrow = {%$row};
                                  @$newrow{keys %$_} = values %$_ unle
+ss $newrow->{$parent_key};
                                  $newrow }  @$expansion ;
                            }
                            @$expanded ];
        push @$expanded,  @$expansion if $count == scalar @$expanded;
      }
      else {
        push @$expanded,  @$expansion ;
      }
    }
    else {
      if ( scalar @$expanded ) {
        map { $_->{$key} = $struct->{$key} } @$expanded;
      }
      else {
        push @$expanded,  { $key => $struct->{$key} };
      }
    }
  }

  return $expanded;
}

[download]

In reply to Re: Expanding / flattening a structure by bangers
in thread Expanding / flattening a structure by jaa

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