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From Adrian Mocanu <amoc...@verticalscope.com>
Subject aggregation in Trident
Date Fri, 07 Feb 2014 17:36:36 GMT
Hi group

Q1: What is the difference between Sum() and Count() as aggregators? I thought they meant
the same thing ie: you count to get the sum.
https://github.com/nathanmarz/storm/wiki/Trident-API-Overview#partitionaggregate gives this
example where both are emitted:
mystream.chainedAgg()
        .partitionAggregate(new Count(), new Fields("count"))
        .partitionAggregate(new Fields("b"), new Sum(), new Fields("sum"))
        .chainEnd()

Q2:
If  you have a tuple with 3 fields like ("name","value","field3") and want to count how many
tuples with the same name you get I can easily use a Count() or Sum() (are they interchangeable?-
see Q1). Problem is after aggregation I get only the sum and not the other fields like "name"
and "field3"
Maybe Trident API wiki page can be updated with such an example

Thanks
-A


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