001/*
002 * Copyright (c) 2007-2015 Concurrent, Inc. All Rights Reserved.
003 *
004 * Project and contact information: http://www.cascading.org/
005 *
006 * This file is part of the Cascading project.
007 *
008 * Licensed under the Apache License, Version 2.0 (the "License");
009 * you may not use this file except in compliance with the License.
010 * You may obtain a copy of the License at
011 *
012 *     http://www.apache.org/licenses/LICENSE-2.0
013 *
014 * Unless required by applicable law or agreed to in writing, software
015 * distributed under the License is distributed on an "AS IS" BASIS,
016 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
017 * See the License for the specific language governing permissions and
018 * limitations under the License.
019 */
020
021package cascading.operation.aggregator;
022
023import java.beans.ConstructorProperties;
024
025import cascading.flow.FlowProcess;
026import cascading.operation.Aggregator;
027import cascading.operation.AggregatorCall;
028import cascading.operation.BaseOperation;
029import cascading.operation.OperationCall;
030import cascading.tuple.Fields;
031import cascading.tuple.Tuple;
032import cascading.util.Pair;
033
034/**
035 * Class Count is an {@link Aggregator} that calculates the number of items in the current group.
036 * </p>
037 * Note the resulting value for count is always a long. So any comparisons should be against a long value.
038 */
039public class Count extends BaseOperation<Pair<Long[], Tuple>> implements Aggregator<Pair<Long[], Tuple>>
040  {
041  /** Field COUNT */
042  public static final String FIELD_NAME = "count";
043
044  /** Constructor Count creates a new Count instance using the default field declaration of name 'count'. */
045  public Count()
046    {
047    super( new Fields( FIELD_NAME, Long.class ) );
048    }
049
050  /**
051   * Constructor Count creates a new Count instance and returns a field with the given fieldDeclaration name.
052   *
053   * @param fieldDeclaration of type Fields
054   */
055  @ConstructorProperties({"fieldDeclaration"})
056  public Count( Fields fieldDeclaration )
057    {
058    super( fieldDeclaration ); // allow ANY number of arguments
059    }
060
061  @Override
062  public void prepare( FlowProcess flowProcess, OperationCall<Pair<Long[], Tuple>> operationCall )
063    {
064    operationCall.setContext( new Pair<Long[], Tuple>( new Long[]{0L}, Tuple.size( 1 ) ) );
065    }
066
067  @Override
068  public void start( FlowProcess flowProcess, AggregatorCall<Pair<Long[], Tuple>> aggregatorCall )
069    {
070    aggregatorCall.getContext().getLhs()[ 0 ] = 0L;
071    }
072
073  @Override
074  public void aggregate( FlowProcess flowProcess, AggregatorCall<Pair<Long[], Tuple>> aggregatorCall )
075    {
076    aggregatorCall.getContext().getLhs()[ 0 ] += 1L;
077    }
078
079  @Override
080  public void complete( FlowProcess flowProcess, AggregatorCall<Pair<Long[], Tuple>> aggregatorCall )
081    {
082    aggregatorCall.getOutputCollector().add( getResult( aggregatorCall ) );
083    }
084
085  protected Tuple getResult( AggregatorCall<Pair<Long[], Tuple>> aggregatorCall )
086    {
087    aggregatorCall.getContext().getRhs().set( 0, aggregatorCall.getContext().getLhs()[ 0 ] );
088
089    return aggregatorCall.getContext().getRhs();
090    }
091  }