io.cdap.cdap.etl.api

Interface Aggregator<GROUP_KEY,GROUP_VALUE,OUT>

Type Parameters:

GROUP_KEY - Type of group key

GROUP_VALUE - Type of values to group

OUT - Type of output object

All Known Implementing Classes:

BatchAggregator

@Beta
public interface Aggregator<GROUP_KEY,GROUP_VALUE,OUT>

Groups all input objects into collections and performs an aggregation on the entire group. Objects that have the same group key are placed into the same group for aggregation.

Method Summary

Modifier and Type	Method and Description
void	aggregate(GROUP_KEY groupKey, Iterator<GROUP_VALUE> groupValues, Emitter<OUT> emitter) Aggregate all objects in the same group into zero or more output objects.
void	groupBy(GROUP_VALUE groupValue, Emitter<GROUP_KEY> emitter) Emit the group key(s) for a given input value.

Method Detail

groupBy

void groupBy(GROUP_VALUE groupValue,
             Emitter<GROUP_KEY> emitter)
      throws Exception

Emit the group key(s) for a given input value. If no group key is emitted, the input value is filtered out. If multiple group keys are emitted, the input value will be present in multiple groups.

Parameters:

groupValue - the value to group

emitter - the emitter to emit zero or more group keys for the input

Throws:

Exception - if there is some error getting the group

aggregate

void aggregate(GROUP_KEY groupKey,
               Iterator<GROUP_VALUE> groupValues,
               Emitter<OUT> emitter)
        throws Exception

Aggregate all objects in the same group into zero or more output objects.

Parameters:

groupKey - the key for the group

groupValues - an iterator over all input objects that have the same group key

emitter - the emitter to emit aggregate values for the group

Throws:

Exception - if there is some error aggregating