com.yahoo.sketches.pig.hll.SketchToEstimateAndErrorBounds Maven / Gradle / Ivy
/*
* Copyright 2017, Yahoo! Inc.
* Licensed under the terms of the Apache License 2.0. See LICENSE file at the project root for terms.
*/
package com.yahoo.sketches.pig.hll;
import java.io.IOException;
import org.apache.pig.EvalFunc;
import org.apache.pig.data.DataByteArray;
import org.apache.pig.data.DataType;
import org.apache.pig.data.Tuple;
import org.apache.pig.data.TupleFactory;
import org.apache.pig.impl.logicalLayer.FrontendException;
import org.apache.pig.impl.logicalLayer.schema.Schema;
import com.yahoo.memory.Memory;
import com.yahoo.sketches.hll.HllSketch;
/**
* This is a User Defined Function (UDF) for obtaining the unique count estimate
* along with a lower and upper bound from an HllSketch.
*
* The result is a tuple with three double values: estimate, lower bound and upper bound.
* The bounds are given at 95.5% confidence.
*
* @author Alexander Saydakov
*/
public class SketchToEstimateAndErrorBounds extends EvalFunc {
@Override
public Tuple exec(final Tuple sketchTuple) throws IOException {
if ((sketchTuple == null) || (sketchTuple.size() == 0)) {
return null;
}
final DataByteArray dba = (DataByteArray) sketchTuple.get(0);
final HllSketch sketch = HllSketch.wrap(Memory.wrap(dba.get()));
final Tuple outputTuple = TupleFactory.getInstance().newTuple(3);
outputTuple.set(0, Double.valueOf(sketch.getEstimate()));
outputTuple.set(1, Double.valueOf(sketch.getLowerBound(2)));
outputTuple.set(2, Double.valueOf(sketch.getUpperBound(2)));
return outputTuple;
}
/**
* The output is a Sketch Result Tuple Schema.
*/
@Override
public Schema outputSchema(final Schema input) {
if (input == null) { return null; }
try {
final Schema tupleSchema = new Schema();
tupleSchema.add(new Schema.FieldSchema("Estimate", DataType.DOUBLE));
tupleSchema.add(new Schema.FieldSchema("LowerBound", DataType.DOUBLE));
tupleSchema.add(new Schema.FieldSchema("UpperBound", DataType.DOUBLE));
return new Schema(new Schema.FieldSchema(getSchemaName(this
.getClass().getName().toLowerCase(), input), tupleSchema, DataType.TUPLE));
} catch (final FrontendException e) {
throw new RuntimeException(e);
}
}
}