src/main/java/com/yahoo/sketches/pig/frequencies/DataToFrequentItemsSketchAlgebraicIntermediateFinal.java

/*
 * Copyright 2015, 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.frequencies;

import java.io.IOException;

import org.apache.log4j.Logger;
import org.apache.pig.EvalFunc;
import org.apache.pig.data.DataBag;
import org.apache.pig.data.DataByteArray;
import org.apache.pig.data.Tuple;

import com.yahoo.sketches.frequencies.ArrayOfItemsSerDe;
import com.yahoo.sketches.frequencies.FrequentItemsSketch;

/**
 * Class used to calculate the intermediate pass (combiner) or the final pass
 * (reducer) of an Algebraic sketch operation. This may be called multiple times
 * (from the mapper and from the reducer). It will receive a bag of values
 * returned by either the Intermediate stage or the Initial stages, so
 * it needs to be able to differentiate between and interpret both types.
 * @param <T> Type of the item
 */
public abstract class DataToFrequentItemsSketchAlgebraicIntermediateFinal<T> extends EvalFunc<Tuple> {

  private int sketchSize_;
  private ArrayOfItemsSerDe<T> serDe_;
  private boolean isFirstCall_ = true;

  /**
   * Default constructor to make pig validation happy.
   */
  public DataToFrequentItemsSketchAlgebraicIntermediateFinal() {}
  
  public DataToFrequentItemsSketchAlgebraicIntermediateFinal(final int sketchSize, final ArrayOfItemsSerDe<T> serDe) {
    sketchSize_ = sketchSize;
    serDe_ = serDe;
  }
  
  @Override
  public Tuple exec(final Tuple inputTuple) throws IOException {
    if (isFirstCall_) {
      Logger.getLogger(getClass()).info("algebraic was used"); // this is to see in the log which way was used by Pig
      isFirstCall_ = false;
    }
    final FrequentItemsSketch<T> sketch = new FrequentItemsSketch<T>(sketchSize_);

    DataBag bag = (DataBag) inputTuple.get(0);
    if (bag == null) {
      throw new IllegalArgumentException("InputTuple.Field0: Bag may not be null");
    }

    for (Tuple dataTuple: bag) {
      Object item = dataTuple.get(0);
      if (item instanceof DataBag) {
        // this is a bag from the Initial function.
        // just insert each item of the tuple into the sketch
        DataToFrequentItemsSketch.updateSketch((DataBag)item, sketch);
      } else if (item instanceof DataByteArray) {
        // This is a sketch from a prior call to the 
        // Intermediate function. merge it with the 
        // current sketch.
        FrequentItemsSketch<T> incomingSketch = Util.deserializeSketchFromTuple(dataTuple, serDe_);
        sketch.merge(incomingSketch);
      } else {
        // we should never get here.
        throw new IllegalArgumentException("InputTuple.Field0: Bag contains unrecognized types: " + item.getClass().getName());
      }
    }
    return Util.serializeSketchToTuple(sketch, serDe_);
  }

}