Re: Reversing Hash

Hi Dave
That doesn't work:
Your script gives me answer without any 'reduction' in rev_hash keys.

$rev_hash{1 20 3} = "key1"
$rev_hash{1 9 17} = "key4 key5"
$rev_hash{1 9 8} = "key3"
$rev_hash{1 30 4 7} = "key2"

Which doesn't reduce the keys to its minimum possible. I like to have keys "3" "1 17" "1 8" and "4" . so the answer should be

$rev_hash{3} = "key1"
$rev_hash{1 17} = "key4 key5"
$rev_hash{1 8} = "key3"
$rev_hash{4} = "key2"

Thanks
artist

Update: I think question is mis-understood by most first-answeres. Above example would make it clear.

Update2: Hofmator gave a more correct solution at Re: Re: Re: Reversing Hash as it reduces most elements in total. I overlooked that earlier and should have produced a better example.

Comment on Re: Reversing Hash

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Re^2: Reversing Hash by Aristotle (Chancellor) on Mar 03, 2003 at 14:30 UTC
You'll have to do that in three steps. First step: `my %hash = ( 'key1' => [1, 20, 3], 'key2' => [1, 30, 4, 7], 'key3' => [1, 9, 8], 'key4' => [1, 9, 17], 'key5' => [1, 9, 17], ); my %rev_hash; while(my ($k, $v) = each %hash) { push @{$rev_hash{$_}}, $k for @$v; }` [download] Now we have this: `%rev_hash = ( '7' => ['key2'], '8' => ['key3'], '30' => ['key2'], '9' => [ 'key3', 'key4', 'key5' ], '1' => [ 'key1', 'key2', 'key3', 'key4', 'key5' ], '17' => [ 'key4', 'key5' ], '3' => ['key1'], '4' => ['key2'], '20' => ['key1'] );` Now let's lump together unique lists of values. I tried a more general approach trying to compare arrays as arrays at first, but it makes things much harder due to double bookkeeping. Since you just want the values concatenated to a string, the approach can be simplified drastically by doing that beforehand. `$_ = join ' ', sort @$_ for values %rev_hash; my %inv_hash; while(my ($k, $v) = each %rev_hash) { push @{$inv_hash{$v}}, $k; }` [download] Almost all the way there: `%inv_hash = ( 'key1' => [ '3', '20' ], 'key3 key4 key5' => ['9'], 'key2' => [ '7', '30', '4' ], 'key3' => ['8'], 'key4 key5' => ['17'], 'key1 key2 key3 key4 key5' => ['1'], );` We need to concatenate and reverse one final time: `$_ = join ' ', sort {$a<=>$b} @$_ for values %inv_hash; my %revinv_hash = reverse %inv_hash;` [download] And now we have: `%revinv_hash = ( '3 20' => 'key1', '8' => 'key3', '9' => 'key3 key4 key5', '1' => 'key1 key2 key3 key4 key5', '17' => 'key4 key5', '4 7 30' => 'key2' );` There you go. Makeshifts last the longest.	[reply] [d/l] [select]

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Re^2: Reversing Hash
by Aristotle (Chancellor) on Mar 03, 2003 at 14:30 UTC

my %hash = (
    'key1' => [1, 20, 3],
    'key2' => [1, 30, 4, 7],
    'key3' => [1, 9, 8],
    'key4' => [1, 9, 17],
    'key5' => [1, 9, 17],
);

my %rev_hash;

while(my ($k, $v) = each %hash) {
    push @{$rev_hash{$_}}, $k for @$v;
}
[download]

%rev_hash = (
	'7'  => ['key2'],
	'8'  => ['key3'],
	'30' => ['key2'],
	'9'  => [ 'key3', 'key4', 'key5' ],
	'1'  => [ 'key1', 'key2', 'key3', 'key4', 'key5' ],
	'17' => [ 'key4', 'key5' ],
	'3'  => ['key1'],
	'4'  => ['key2'],
	'20' => ['key1']
);

$_ = join ' ', sort @$_  for values %rev_hash;

my %inv_hash;
while(my ($k, $v) = each %rev_hash) {
    push @{$inv_hash{$v}}, $k;
}
[download]

%inv_hash = (
	'key1'                     => [ '3', '20' ],
	'key3 key4 key5'           => ['9'],
	'key2'                     => [ '7', '30', '4' ],
	'key3'                     => ['8'],
	'key4 key5'                => ['17'],
	'key1 key2 key3 key4 key5' => ['1'],
);

$_ = join ' ', sort {$a<=>$b} @$_  for values %inv_hash;

my %revinv_hash = reverse %inv_hash;
[download]

%revinv_hash = (
	'3 20'   => 'key1',
	'8'      => 'key3',
	'9'      => 'key3 key4 key5',
	'1'      => 'key1 key2 key3 key4 key5',
	'17'     => 'key4 key5',
	'4 7 30' => 'key2'
);

Makeshifts last the longest.

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