code: public DistinctOperator<T> distinct(int... fields) {
  		return new DistinctOperator<>(this, new Keys.ExpressionKeys<>(fields, getType()), Utils.getCallLocationName());
  	}
docs: Returns a distinct set of a {@link Tuple} {@link DataSet} using field position keys.
  
  <p>The field position keys specify the fields of Tuples on which the decision is made if two Tuples are distinct or
  not.
  
  <p>Note: Field position keys can only be specified for Tuple DataSets.
  
  @param fields One or more field positions on which the distinction of the DataSet is decided.
  @return A DistinctOperator that represents the distinct DataSet.