http://www.perlmonks.org?node_id=660559


in reply to Re^2: hash from CSV-like structure
in thread hash from CSV-like structure

To avoid undef warnings, you might want to make the duplicate check more like this: 
    next if $results{$val} 
     and $hash->{$key1}
     and $hash->{$key1}->{$key2};

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