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Efficient 'uniq' Snippet

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        This snippet will quickly uniq an unsorted array; in other words, remove duplicates.   (note: for large arrays, it may be more efficient to sort the array first and simply keep track of consecutive dups instead of using a hash.)

  # Input: @list
  # Output: @uniqed
  my %u = ();
  @uniqed = grep {defined} map {
      if (exists $u{$_}) { undef; } else { $u{$_}=undef;$_; }
    } @list;
  undef %u;