Hi.

This solution assumes that you don't mind duplicate values (i.e. where two unique keys from %hash have the same value) being pushed onto an array.

Also, feel free to change the value of $; to whatever you like if a space isn't suitable.

use strict;

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

{
  local ($;) = " ";

  while (my ($k, $v) = each %hash) {
    push @{$rev_hash{"@{$v}"}}, $k;
  }
  
  while (my ($k, $v) = each %rev_hash) {
    print qq(\$rev_hash{$k} = "@{$v}"\n);
  }
}
[download]

Cheers,

-- Dave :-)

$q=[split+qr,,,q,~swmi,.$,],+s.$.Em~w^,,.,s,.,$&&$$q[pos],eg,print

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

1. 3
2. 4
3. 8
4. 17

-- Hofmator