27.13.4 Union of PGX Frames
You can join two PgxFrames that have compatible columns (that is,
      same type and order).
               
opg4j> <firstFrame>.union(<secondFrame>).print()<firstFrame>.union(<secondFrame>).print();<first_frame>.union(<second_frame>).print()The rows of the resulting
          PgxFrame are the union of the rows from the two original frames.
                  
Parent topic: PgxFrames Tabular Data-Structure