001 /* 002 * Copyright (c) 2007-2014 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 }