foreach my $string ( @data ) {   # dedupe data and sanity check.
      next if !defined ($string);   # should never be true.
      next if $seen{ $string }[ 0 ] == 1; # check %seen hash / array for dupe
      $seen{ $string }[ 0 ] = 1;    # define hash of array and assign check to it.
      $seen{ $string }[ 1 ] = $key; # add word from line to hash for reference.
   }