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group_by:
An optional list of attributes over which the grouping should occur.aggregations:
A list if elements where each element contains up to four string:- The name of the aggregate function, e.g. MAX
- The input attribute over which the aggregation should be done
- The name of the output attribute for this aggregation
- The optional type of the output
dumpAtValueCount:
This parameter is used in the interval approach. Here a result is generated, each time an aggregation cannot be changed anymore. This leads to fewer results with a larger validity. With this parameter the production rate can be raised. A value of 1 means, that for every new element the aggregation operator receives new output elements are generated. This leads to more results with a shorter validity.outputPA
: This parameter allow to dump partial aggregates instead of evaluted values. The partial aggregates can be send to other aggregation operators and do a final aggregation (e.g. in case of distribution). The input schema of an aggregate operator that read partial aggregates must state a datatype that is a partial aggregated (see example below). Remark: Aggregate has one input and requires ordered input. To combine different parital aggregations e.g. a union operator is needed to reorder the input elements.drainAtDone
: Boolean, default true: If done is called, all not already written elements will be written.drainAtClose
: Boolean, default false: If close is called, all not already written elements will be written.FastGrouping
: Use hash code instead of compare to create group. Potentially unsafe!
Aggregation Functions
The set of aggregate functions is extensible. The following list is in the core Odysseus:
MAX
: The maximum elementMIN
: The minimum elementAVG
: The average elementSUM
: The sum of all elementsCOUNT
: The number of elementsMEDIAN
: The median elementSTDDEV
: The standard deviation
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FIRST
: The first elementLAST
: The last elementNTH
: The nth elementRATE
: The number of elements per time unitNEST
: Nest the attribute values in a listCOMPLETENESS
: Ratio of NULL-value elements to number of elements
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