How can I remove elements from a stream

Question

I currently have an order object. We can assume it has three fields called orderId, state and price.

class Order
{
    public int orderId;
    public String state;
    public int filled;
}

Through out the life time of the order the state and filled quantity will change. Each time there is a field change we push it to the esper runtime via:

Order o .....;
epService.EPRuntime.SendEvent(o);

Now each time the order is added via SendEvent its a different object than the previous order object( ie not a reference). This means the old order object should no longer be in stream for statements to see

I would like statements like the one below to only operate on the most recent version of the Order in the stream, ie conceptually there should only be one order object for each physical order in the stream.

 "select filled from OrderStream.win:keepall() where orderId= 1234"

Is there a way to remove old Order objects? Can I use a reference so I just update the old order object and then push it again? Is there another way??

I'm currently using Nesper

score 1 · Answer 1 · answered Mar 28 '14 at 17:26

1

You could create a named window that holds unique events (older duplicates are evicted)

something like :

"create window OrderWin.std:unique(orderId) as Order"
"insert into "OrderWin select * from Order"
"select * from OrderWin where ..."

answered Mar 28 '14 at 17:26

R Dub

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score 0 · Answer 2 · answered Jun 25 '14 at 00:08

Another answer is to change the window. Keeping all events probably isn't what you wanted. Try using a different window, for example...

Let's say you only wanted the last trade per symbol. You could do the following:

select * from tradeEvent.std:unique(symbol)

This keeps only the last event for each event matching a given symbol.

How can I remove elements from a stream

2 Answers2