stream.scotty.core.windowFunction

Interface AggregateFunction<InputType,PartialAggregateType,FinalAggregateType>

All Superinterfaces:

java.io.Serializable

All Known Subinterfaces:

CommutativeAggregateFunction<InputType,PartialAggregateType,FinalAggregateType>, InvertibleAggregateFunction<InputType,PartialAggregateType,FinalAggregateType>, InvertibleReduceAggregateFunction<Input>, ReduceAggregateFunction<InputType>

All Known Implementing Classes:

MaxWindowFunction, MinWindowFunction, QuantileWindowFunction, SumAggregation, SumWindowFunction

public interface AggregateFunction<InputType,PartialAggregateType,FinalAggregateType>
extends java.io.Serializable

Method Summary

Modifier and Type	Method and Description
PartialAggregateType	combine(PartialAggregateType partialAggregate1, PartialAggregateType partialAggregate2) Computes the combined aggregate from partial aggregates.
PartialAggregateType	lift(InputType inputTuple) Transforms a tuple to a partial aggregate.
FinalAggregateType	lower(PartialAggregateType aggregate) Transforms a partial aggregate to a final aggregate.

Method Detail

lift

PartialAggregateType lift(InputType inputTuple)

Transforms a tuple to a partial aggregate. For example, consider an average computation. If a tuple ⟨p,v⟩ contains its position p and a value v, the lift function will transform it to ⟨sum←v, count←1⟩, which is the partial aggregate of that one tuple.

Parameters:

inputTuple - input Tuple

Returns:

PartialAggregate

combine

PartialAggregateType combine(PartialAggregateType partialAggregate1,
                             PartialAggregateType partialAggregate2)

Computes the combined aggregate from partial aggregates. Each incremental aggregation step results in one call of the combine function.

Parameters:

partialAggregate1 -

partialAggregate2 -

Returns:

combined PartialAggregate

lower

FinalAggregateType lower(PartialAggregateType aggregate)

Transforms a partial aggregate to a final aggregate. In our example, the lower function computes the average from sum and count: ⟨sum, count⟩ 7→ sum/count.

Parameters:

aggregate -

Returns:

final Aggregate