Very good point. This (not very optimised) code would flip and create the data
structure. It is a bit cheesy though:
use Data::Dumper;
my %hash = ( 'a'=>1, 'b'=>2, 'c'=>3, 'd'=>4, 'e'=>4, 'f'=>4);
my %by_value = flip(%hash);
print Data::Dumper->Dump([\%hash], ['*hash']);
print Data::Dumper->Dump([\%by_value], ['*by_value']);
sub flip
{
my($k, $v, %hash);
my %foo = @_;
$hash{$v} = defined $hash{$v} ?
[ ref $hash{$v} ? @{$hash{$v}} : $hash{$v} , $k ]
+:
$k while (($k,$v) = each %foo);
return %hash;
}
Results:%hash = (
'a' => 1,
'b' => 2,
'c' => 3,
'd' => 4,
'e' => 4,
'f' => 4
);
%by_value = (
1 => 'a',
2 => 'b',
3 => 'c',
4 => [
'd',
'e',
'f'
]
);
