src/main/java/org/apache/datasketches/pig/tuple/ArrayOfDoublesSketchToMeans.java

/*
 * 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.datasketches.pig.tuple;

import java.io.IOException;

import org.apache.commons.math3.stat.descriptive.SummaryStatistics;
import org.apache.datasketches.memory.Memory;
import org.apache.datasketches.tuple.ArrayOfDoublesSketch;
import org.apache.datasketches.tuple.ArrayOfDoublesSketches;
import org.apache.pig.EvalFunc;
import org.apache.pig.data.DataByteArray;
import org.apache.pig.data.Tuple;
import org.apache.pig.data.TupleFactory;

/**
 * This UDF converts an ArrayOfDoubles sketch to mean values.
 * The result will be a tuple with N double values, where
 * N is the number of double values kept in the sketch per key.
 */
public class ArrayOfDoublesSketchToMeans extends EvalFunc<Tuple> {

  @Override
  public Tuple exec(final Tuple input) throws IOException {
    if ((input == null) || (input.size() == 0)) {
      return null;
    }

    final DataByteArray dba = (DataByteArray) input.get(0);
    final ArrayOfDoublesSketch sketch = ArrayOfDoublesSketches.wrapSketch(Memory.wrap(dba.get()));

    if (sketch.getRetainedEntries() < 1) {
      return null;
    }

    final SummaryStatistics[] summaries = ArrayOfDoublesSketchStats.sketchToSummaryStatistics(sketch);

    final Tuple means = TupleFactory.getInstance().newTuple(sketch.getNumValues());
    for (int i = 0; i < sketch.getNumValues(); i++) {
      means.set(i, summaries[i].getMean());
    }
    return means;
  }

}