help needed in retrieving the hash key

[singam]

hai monks,
Is there any efficient way or algorithm to retrive the key from the hash based on the values.
both the keys and the values are unique.

[murugu]

Hi,

As you mentioned that keys and values are unique,

my %hash2 = reverse %hash1;

Now the keys and values got interchanged.

[tirwhan]

%reverse_hash = reverse %original_hash

For more, see perldoc -q "hash element by value"</p>

[inman]

An alternative method uses the each and keys functions to iterate over a hash and locate the keys. This has the advantage of coping with the more general case wher multiple instances of a value in addition to not requiring the storage of another hash.

my @keys = qw ( a b c d e f g h i j);
my @vals = qw ( 1 1 1 4 5 6 7 8 9 0);
my %hash;

@hash{@keys} = @vals;
my @ones = grep {(each %hash)[1] == 1} keys %hash;

print "@ones\n";

Inverting the hash as shown previously is a better method if you are OK with the storage overhead and you will be doing multiple retrievals.

[jwkrahn]

$ perl -le'
my %x = qw/ one two three four five six seven eight /;
print ${ { reverse %x } }{ six };
'
five