/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.hive.contrib.udaf.example;
import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.UDAF;
import org.apache.hadoop.hive.ql.exec.UDAFEvaluator;
/**
* This is a simple UDAF that calculates average.
*
* It should be very easy to follow and can be used as an example for writing
* new UDAFs.
*
* Note that Hive internally uses a different mechanism (called GenericUDAF) to
* implement built-in aggregation functions, which are harder to program but
* more efficient.
*
*/
@Description(name = "example_avg",
value = "_FUNC_(col) - Example UDAF to compute average")
public final class UDAFExampleAvg extends UDAF {
/**
* The internal state of an aggregation for average.
*
* Note that this is only needed if the internal state cannot be represented
* by a primitive.
*
* The internal state can also contains fields with types like
* ArrayList<String> and HashMap<String,Double> if needed.
*/
public static class UDAFAvgState {
private long mCount;
private double mSum;
}
/**
* The actual class for doing the aggregation. Hive will automatically look
* for all internal classes of the UDAF that implements UDAFEvaluator.
*/
public static class UDAFExampleAvgEvaluator implements UDAFEvaluator {
UDAFAvgState state;
public UDAFExampleAvgEvaluator() {
super();
state = new UDAFAvgState();
init();
}
/**
* Reset the state of the aggregation.
*/
public void init() {
state.mSum = 0;
state.mCount = 0;
}
/**
* Iterate through one row of original data.
*
* The number and type of arguments need to the same as we call this UDAF
* from Hive command line.
*
* This function should always return true.
*/
public boolean iterate(Double o) {
if (o != null) {
state.mSum += o;
state.mCount++;
}
return true;
}
/**
* Terminate a partial aggregation and return the state. If the state is a
* primitive, just return primitive Java classes like Integer or String.
*/
public UDAFAvgState terminatePartial() {
// This is SQL standard - average of zero items should be null.
return state.mCount == 0 ? null : state;
}
/**
* Merge with a partial aggregation.
*
* This function should always have a single argument which has the same
* type as the return value of terminatePartial().
*/
public boolean merge(UDAFAvgState o) {
if (o != null) {
state.mSum += o.mSum;
state.mCount += o.mCount;
}
return true;
}
/**
* Terminates the aggregation and return the final result.
*/
public Double terminate() {
// This is SQL standard - average of zero items should be null.
return state.mCount == 0 ? null : Double.valueOf(state.mSum
/ state.mCount);
}
}
private UDAFExampleAvg() {
// prevent instantiation
}
}