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    
021    package cascading.operation.aggregator;
022    
023    import java.beans.ConstructorProperties;
024    
025    import cascading.flow.FlowProcess;
026    import cascading.operation.Aggregator;
027    import cascading.operation.AggregatorCall;
028    import cascading.operation.BaseOperation;
029    import cascading.operation.OperationCall;
030    import cascading.tuple.Fields;
031    import cascading.tuple.Tuple;
032    import 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     */
039    public 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      }