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How do I look up a hash element by value?

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How do I look up a hash element by value?

Create a reverse hash:

    %by_value = reverse %by_key;
    $key = $by_value{$value};

That's not particularly efficient. It would be more space-efficient to use:

    while (($key, $value) = each %by_key) {
        $by_value{$value} = $key;

If your hash could have repeated values, the methods above will only find one of the associated keys. This may or may not worry you.

Source: Perl FAQ: Data Manipulation
Copyright: Copyright (c) 1997 Tom Christiansen and Nathan Torkington.
Next: How can I know how many entries are in a hash?

Previous: What happens if I add or remove keys from a hash while iterating over it?

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