src/main/java/org/apache/datasketches/pig/frequencies/DataToFrequentItemsSketch.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.frequencies;

import java.io.IOException;

import org.apache.datasketches.ArrayOfItemsSerDe;
import org.apache.datasketches.frequencies.ItemsSketch;
import org.apache.log4j.Logger;
import org.apache.pig.Accumulator;
import org.apache.pig.EvalFunc;
import org.apache.pig.backend.executionengine.ExecException;
import org.apache.pig.data.DataBag;
import org.apache.pig.data.Tuple;

/**
 * This is a generic implementation to be specialized in concrete UDFs
 * @param <T> type of item
 */
public abstract class DataToFrequentItemsSketch<T> extends EvalFunc<Tuple> implements Accumulator<Tuple> {

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

  /**
   * Constructs a function given a sketch size and serde
   * @param sketchSize parameter controlling the size of the sketch and the accuracy
   * @param serDe an instance of ArrayOfItemsSerDe to serialize and deserialize arrays of items
   */
  public DataToFrequentItemsSketch(final int sketchSize, final ArrayOfItemsSerDe<T> serDe) {
    super();
    sketchSize_ = sketchSize;
    serDe_ = serDe;
  }

  @Override
  public void accumulate(final Tuple inputTuple) throws IOException {
    if (isFirstCall_) {
      // this is to see in the log which way was used by Pig
      Logger.getLogger(getClass()).info("accumulate was used");
      isFirstCall_ = false;
    }
    if (accumSketch_ == null) {
      accumSketch_ = new ItemsSketch<T>(sketchSize_);
    }
    if (inputTuple.size() != 1) {
      throw new IllegalArgumentException("Input tuple must have 1 bag");
    }
    final DataBag bag = (DataBag) inputTuple.get(0);
    updateSketch(bag, accumSketch_);
  }

  @Override
  public void cleanup() {
    accumSketch_ = null;
  }

  @Override
  public Tuple getValue() {
    if (accumSketch_ == null) {
      accumSketch_ = new ItemsSketch<T>(sketchSize_);
    }
    final Tuple outputTuple;
    try {
      outputTuple = Util.serializeSketchToTuple(accumSketch_, serDe_);
    } catch (final ExecException ex) {
      throw new RuntimeException("Pig Error: " + ex.getMessage(), ex);
    }
    return outputTuple;
  }

  @Override
  public Tuple exec(final Tuple inputTuple) throws IOException {
    if (isFirstCall_) {
      // this is to see in the log which way was used by Pig
      Logger.getLogger(getClass()).info("exec was used");
      isFirstCall_ = false;
    }
    if ((inputTuple == null) || (inputTuple.size() == 0)) {
      return null;
    }
    accumulate(inputTuple);
    final Tuple outputTuple = getValue();
    cleanup();
    return outputTuple;
  }

  static <T> void updateSketch(final DataBag bag, final ItemsSketch<T> sketch) throws ExecException {
    if (bag == null) {
      throw new IllegalArgumentException("InputTuple.Field0: Bag may not be null");
    }
    for (final Tuple tuple: bag) {
      if (tuple.size() != 1 && tuple.size() != 2) {
        throw new IllegalArgumentException("Inner tuple of input bag must have 1 or 2 fields.");
      }
      @SuppressWarnings("unchecked")
      final T key = (T) tuple.get(0);
      if (key == null) { continue; }
      final long value = tuple.size() == 2 ? (long) tuple.get(1) : 1;
      sketch.update(key, value);
    }
  }

}