org.apache.hadoop.hive.ql.udf.generic.GenericUDAFCovarianceSample Maven / Gradle / Ivy
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* 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.ql.udf.generic;
import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.UDFArgumentTypeException;
import org.apache.hadoop.hive.ql.metadata.HiveException;
import org.apache.hadoop.hive.ql.parse.SemanticException;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
import org.apache.hadoop.hive.serde2.typeinfo.PrimitiveTypeInfo;
import org.apache.hadoop.hive.serde2.typeinfo.TypeInfo;
/**
* Compute the sample covariance by extending GenericUDAFCovariance and overriding
* the terminate() method of the evaluator.
*
*/
@Description(name = "covar_samp",
value = "_FUNC_(x,y) - Returns the sample covariance of a set of number pairs",
extended = "The function takes as arguments any pair of numeric types and returns a double.\n"
+ "Any pair with a NULL is ignored. If the function is applied to an empty set, NULL\n"
+ "will be returned. Otherwise, it computes the following:\n"
+ " (SUM(x*y)-SUM(x)*SUM(y)/COUNT(x,y))/(COUNT(x,y)-1)\n"
+ "where neither x nor y is null.")
public class GenericUDAFCovarianceSample extends GenericUDAFCovariance {
@Override
public GenericUDAFEvaluator getEvaluator(TypeInfo[] parameters)
throws SemanticException {
if (parameters.length != 2) {
throw new UDFArgumentTypeException(parameters.length - 1,
"Exactly two arguments are expected.");
}
if (parameters[0].getCategory() != ObjectInspector.Category.PRIMITIVE) {
throw new UDFArgumentTypeException(0,
"Only primitive type arguments are accepted but "
+ parameters[0].getTypeName() + " is passed.");
}
if (parameters[1].getCategory() != ObjectInspector.Category.PRIMITIVE) {
throw new UDFArgumentTypeException(1,
"Only primitive type arguments are accepted but "
+ parameters[1].getTypeName() + " is passed.");
}
switch (((PrimitiveTypeInfo) parameters[0]).getPrimitiveCategory()) {
case BYTE:
case SHORT:
case INT:
case LONG:
case FLOAT:
case DOUBLE:
case TIMESTAMP:
case DECIMAL:
switch (((PrimitiveTypeInfo) parameters[1]).getPrimitiveCategory()) {
case BYTE:
case SHORT:
case INT:
case LONG:
case FLOAT:
case DOUBLE:
case TIMESTAMP:
case DECIMAL:
return new GenericUDAFCovarianceSampleEvaluator();
case STRING:
case BOOLEAN:
case DATE:
default:
throw new UDFArgumentTypeException(1,
"Only numeric or string type arguments are accepted but "
+ parameters[1].getTypeName() + " is passed.");
}
case STRING:
case BOOLEAN:
case DATE:
default:
throw new UDFArgumentTypeException(0,
"Only numeric or string type arguments are accepted but "
+ parameters[0].getTypeName() + " is passed.");
}
}
/**
* Compute the sample covariance by extending GenericUDAFCovarianceEvaluator and
* overriding the terminate() method of the evaluator.
*/
public static class GenericUDAFCovarianceSampleEvaluator extends
GenericUDAFCovarianceEvaluator {
@Override
public Object terminate(AggregationBuffer agg) throws HiveException {
StdAgg myagg = (StdAgg) agg;
if (myagg.count == 0) { // SQL standard - return null for zero elements
return null;
} else {
if (myagg.count > 1) {
getResult().set(myagg.covar / (myagg.count - 1));
} else { // the covariance of a singleton set is always 0
getResult().set(0);
}
return getResult();
}
}
}
}