Sum (hopping window)

Sums a value over the events alive at each moment; after a hopping window, that is a sum per hop.

After HoppingWindowLifetime(4, 2) each event lives for 4 ticks starting on a 2-tick boundary, so consecutive hops overlap and an event counts in two of them.

In the diagram the result is 3 in [2,4) (a:1 and b:2), 6 in [4,6) (a:3 joins them), 3 in [6,8) (only a:3), 4 in [8,10), 9 in [10,12) (b:4 and a:5) and 5 in [12,14).

Each result is emitted as a start edge and an end edge: the aggregate cannot know when the set of alive events will next change.

See also: HoppingWindowLifetime, Count (tumbling window), GroupApply