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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 java.util.ArrayList;
import java.util.List;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
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.ql.util.JavaDataModel;
import org.apache.hadoop.hive.serde2.io.DoubleWritable;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspectorFactory;
import org.apache.hadoop.hive.serde2.objectinspector.PrimitiveObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.StandardListObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.primitive.PrimitiveObjectInspectorFactory;
import org.apache.hadoop.hive.serde2.objectinspector.primitive.PrimitiveObjectInspectorUtils;
import org.apache.hadoop.hive.serde2.typeinfo.PrimitiveTypeInfo;
import org.apache.hadoop.hive.serde2.typeinfo.TypeInfo;
/**
* Computes an approximate histogram of a numerical column using a user-specified number of bins.
*
* The output is an array of (x,y) pairs as Hive struct objects that represents the histogram's
* bin centers and heights.
*/
@Description(name = "histogram_numeric",
value = "_FUNC_(expr, nb) - Computes a histogram on numeric 'expr' using nb bins.",
extended = "Example:\n"
+ "> SELECT histogram_numeric(val, 3) FROM src;\n"
+ "[{\"x\":100,\"y\":14.0},{\"x\":200,\"y\":22.0},{\"x\":290.5,\"y\":11.0}]\n"
+ "The return value is an array of (x,y) pairs representing the centers of the "
+ "histogram's bins. As the value of 'nb' is increased, the histogram approximation"
+ "gets finer-grained, but may yield artifacts around outliers. In practice, 20-40 "
+ "histogram bins appear to work well, with more bins being required for skewed or "
+ "smaller datasets. Note that this function creates a histogram with non-uniform "
+ "bin widths. It offers no guarantees in terms of the mean-squared-error of the "
+ "histogram, but in practice is comparable to the histograms produced by the R/S-Plus"
+ "statistical computing packages.")
public class GenericUDAFHistogramNumeric extends AbstractGenericUDAFResolver {
// class static variables
static final Log LOG = LogFactory.getLog(GenericUDAFHistogramNumeric.class.getName());
@Override
public GenericUDAFEvaluator getEvaluator(TypeInfo[] parameters) throws SemanticException {
if (parameters.length != 2) {
throw new UDFArgumentTypeException(parameters.length - 1,
"Please specify exactly two arguments.");
}
// validate the first parameter, which is the expression to compute over
if (parameters[0].getCategory() != ObjectInspector.Category.PRIMITIVE) {
throw new UDFArgumentTypeException(0,
"Only primitive type arguments are accepted but "
+ parameters[0].getTypeName() + " was passed as parameter 1.");
}
switch (((PrimitiveTypeInfo) parameters[0]).getPrimitiveCategory()) {
case BYTE:
case SHORT:
case INT:
case LONG:
case FLOAT:
case DOUBLE:
case TIMESTAMP:
case DECIMAL:
break;
case STRING:
case BOOLEAN:
case DATE:
default:
throw new UDFArgumentTypeException(0,
"Only numeric type arguments are accepted but "
+ parameters[0].getTypeName() + " was passed as parameter 1.");
}
// validate the second parameter, which is the number of histogram bins
if (parameters[1].getCategory() != ObjectInspector.Category.PRIMITIVE) {
throw new UDFArgumentTypeException(1,
"Only primitive type arguments are accepted but "
+ parameters[1].getTypeName() + " was passed as parameter 2.");
}
if( ((PrimitiveTypeInfo) parameters[1]).getPrimitiveCategory()
!= PrimitiveObjectInspector.PrimitiveCategory.INT) {
throw new UDFArgumentTypeException(1,
"Only an integer argument is accepted as parameter 2, but "
+ parameters[1].getTypeName() + " was passed instead.");
}
return new GenericUDAFHistogramNumericEvaluator();
}
/**
* Construct a histogram using an algorithm described by Ben-Haim and Tom-Tov.
*
* The algorithm is a heuristic adapted from the following paper:
* Yael Ben-Haim and Elad Tom-Tov, "A streaming parallel decision tree algorithm",
* J. Machine Learning Research 11 (2010), pp. 849--872. Although there are no approximation
* guarantees, it appears to work well with adequate data and a large (e.g., 20-80) number
* of histogram bins.
*/
public static class GenericUDAFHistogramNumericEvaluator extends GenericUDAFEvaluator {
// For PARTIAL1 and COMPLETE: ObjectInspectors for original data
private PrimitiveObjectInspector inputOI;
private transient PrimitiveObjectInspector nbinsOI;
// For PARTIAL2 and FINAL: ObjectInspectors for partial aggregations (list of doubles)
private transient StandardListObjectInspector loi;
@Override
public ObjectInspector init(Mode m, ObjectInspector[] parameters) throws HiveException {
super.init(m, parameters);
// init input object inspectors
if (m == Mode.PARTIAL1 || m == Mode.COMPLETE) {
assert(parameters.length == 2);
inputOI = (PrimitiveObjectInspector) parameters[0];
nbinsOI = (PrimitiveObjectInspector) parameters[1];
} else {
loi = (StandardListObjectInspector) parameters[0];
}
// init output object inspectors
if (m == Mode.PARTIAL1 || m == Mode.PARTIAL2) {
// The output of a partial aggregation is a list of doubles representing the
// histogram being constructed. The first element in the list is the user-specified
// number of bins in the histogram, and the histogram itself is represented as (x,y)
// pairs following the first element, so the list length should *always* be odd.
return ObjectInspectorFactory.getStandardListObjectInspector(
PrimitiveObjectInspectorFactory.writableDoubleObjectInspector);
} else {
// The output of FINAL and COMPLETE is a full aggregation, which is a
// list of DoubleWritable structs that represent the final histogram as
// (x,y) pairs of bin centers and heights.
ArrayList foi = new ArrayList();
foi.add(PrimitiveObjectInspectorFactory.writableDoubleObjectInspector);
foi.add(PrimitiveObjectInspectorFactory.writableDoubleObjectInspector);
ArrayList fname = new ArrayList();
fname.add("x");
fname.add("y");
return ObjectInspectorFactory.getStandardListObjectInspector(
ObjectInspectorFactory.getStandardStructObjectInspector(fname, foi) );
}
}
@Override
public Object terminatePartial(AggregationBuffer agg) throws HiveException {
// Return a single ArrayList where the first element is the number of histogram bins,
// and subsequent elements represent histogram (x,y) pairs.
StdAgg myagg = (StdAgg) agg;
return myagg.histogram.serialize();
}
@Override
public Object terminate(AggregationBuffer agg) throws HiveException {
StdAgg myagg = (StdAgg) agg;
if (myagg.histogram.getUsedBins() < 1) { // SQL standard - return null for zero elements
return null;
} else {
ArrayList result = new ArrayList();
for(int i = 0; i < myagg.histogram.getUsedBins(); i++) {
DoubleWritable[] bin = new DoubleWritable[2];
bin[0] = new DoubleWritable(myagg.histogram.getBin(i).x);
bin[1] = new DoubleWritable(myagg.histogram.getBin(i).y);
result.add(bin);
}
return result;
}
}
@Override
public void merge(AggregationBuffer agg, Object partial) throws HiveException {
if(partial == null) {
return;
}
List partialHistogram = (List) loi.getList(partial);
StdAgg myagg = (StdAgg) agg;
myagg.histogram.merge(partialHistogram);
}
@Override
public void iterate(AggregationBuffer agg, Object[] parameters) throws HiveException {
assert (parameters.length == 2);
if(parameters[0] == null || parameters[1] == null) {
return;
}
StdAgg myagg = (StdAgg) agg;
// Parse out the number of histogram bins only once, if we haven't already done
// so before. We need at least 2 bins; otherwise, there is no point in creating
// a histogram.
if(!myagg.histogram.isReady()) {
int nbins = PrimitiveObjectInspectorUtils.getInt(parameters[1], nbinsOI);
if(nbins < 2) {
throw new HiveException(getClass().getSimpleName() + " needs nbins to be at least 2,"
+ " but you supplied " + nbins + ".");
}
// allocate memory for the histogram bins
myagg.histogram.allocate(nbins);
}
// Process the current data point
double v = PrimitiveObjectInspectorUtils.getDouble(parameters[0], inputOI);
myagg.histogram.add(v);
}
// Aggregation buffer definition and manipulation methods
@AggregationType(estimable = true)
static class StdAgg extends AbstractAggregationBuffer {
NumericHistogram histogram; // the histogram object
@Override
public int estimate() {
return JavaDataModel.get().lengthFor(histogram);
}
};
@Override
public AggregationBuffer getNewAggregationBuffer() throws HiveException {
StdAgg result = new StdAgg();
reset(result);
return result;
}
@Override
public void reset(AggregationBuffer agg) throws HiveException {
StdAgg myagg = (StdAgg) agg;
myagg.histogram = new NumericHistogram();
myagg.histogram.reset();
}
}
}
