I am using a Window which keeps 5 rows with one field called 'Value".
Is there a way I can take the average of these five values and pass it to the next stream?
You can just aggregate by a dummy constant to group all the rows. For example
CREATE INPUT WINDOW In1 SCHEMA (Value integer) PRIMARY KEY (Value) KEEP ALL;
CREATE OUTPUT WINDOW Avg
PRIMARY KEY DEDUCED
AS SELECT 1 DummyKey, avg(In1.Value) AvgVal FROM In1 GROUP BY 1;