code: public <R> JoinOperatorSets<T, R> join(DataSet<R> other) {
  		return new JoinOperatorSets<T, R>(this, other);
  	}
docs: Initiates a Join transformation. <br/>
  A Join transformation joins the elements of two
  {@link DataSet DataSets} on key equality and provides multiple ways to combine
  joining elements into one DataSet.</br>
  
  This method returns a {@link JoinOperatorSets} on which
  {@link JoinOperatorSets#where()} needs to be called to define the join key of the first
  joining (i.e., this) DataSet.
  
  @param other The other DataSet with which this DataSet is joined.
  @return A JoinOperatorSets to continue the definition of the Join transformation.
  
  @see JoinOperatorSets
  @see JoinOperator
  @see DataSet