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Hive User Defined Aggregate Functions in Big Data Hadoop

UDAF-User Defined Aggregate Functions.

COUNT, AVG, SUM, MIN, and MAX

Create a Java class which extends org.apache.hadoop.hive.ql.exec.hive.UDAF;

Create an inner class which implements UDAFEvaluator;

Implement five methods ()

init() – The init() method initializes the evaluator and resets its internal state. We are using new Column() in the code below to indicate that no values have been aggregated yet.

iterate() – this method is called every time there is a new value to be aggregated. The evaulator should update its internal state with the result of performing the aggregation (we are doing sum – see below). We return true to indicate that the input was valid.

terminatePartial() – this method is called when Hive wants a result for the partial aggregation. The method must return an object that encapsulates the state of the aggregation.

merge() – this method is called when Hive decides to combine one partial aggregation with another.

terminate() – this method is called when the final result of the aggregation is needed.