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7ValueAggregatorReducer (Hadoop 0.20.1 API)
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79  SUMMARY:&nbsp;NESTED&nbsp;|&nbsp;<A HREF="#fields_inherited_from_class_org.apache.hadoop.mapred.lib.aggregate.ValueAggregatorJobBase">FIELD</A>&nbsp;|&nbsp;<A HREF="#constructor_summary">CONSTR</A>&nbsp;|&nbsp;<A HREF="#method_summary">METHOD</A></FONT></TD>
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90<FONT SIZE="-1">
91org.apache.hadoop.mapred.lib.aggregate</FONT>
92<BR>
93Class ValueAggregatorReducer&lt;K1 extends <A HREF="../../../../../../org/apache/hadoop/io/WritableComparable.html" title="interface in org.apache.hadoop.io">WritableComparable</A>,V1 extends <A HREF="../../../../../../org/apache/hadoop/io/Writable.html" title="interface in org.apache.hadoop.io">Writable</A>&gt;</H2>
94<PRE>
95<A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">java.lang.Object</A>
96  <IMG SRC="../../../../../../resources/inherit.gif" ALT="extended by "><A HREF="../../../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorJobBase.html" title="class in org.apache.hadoop.mapred.lib.aggregate">org.apache.hadoop.mapred.lib.aggregate.ValueAggregatorJobBase</A>&lt;K1,V1&gt;
97      <IMG SRC="../../../../../../resources/inherit.gif" ALT="extended by "><B>org.apache.hadoop.mapred.lib.aggregate.ValueAggregatorReducer&lt;K1,V1&gt;</B>
98</PRE>
99<DL>
100<DT><B>All Implemented Interfaces:</B> <DD><A HREF="http://java.sun.com/javase/6/docs/api/java/io/Closeable.html?is-external=true" title="class or interface in java.io">Closeable</A>, <A HREF="../../../../../../org/apache/hadoop/mapred/JobConfigurable.html" title="interface in org.apache.hadoop.mapred">JobConfigurable</A>, <A HREF="../../../../../../org/apache/hadoop/mapred/Mapper.html" title="interface in org.apache.hadoop.mapred">Mapper</A>&lt;K1,V1,<A HREF="../../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</A>,<A HREF="../../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</A>&gt;, <A HREF="../../../../../../org/apache/hadoop/mapred/Reducer.html" title="interface in org.apache.hadoop.mapred">Reducer</A>&lt;<A HREF="../../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</A>,<A HREF="../../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</A>,<A HREF="../../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</A>,<A HREF="../../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</A>&gt;</DD>
101</DL>
102<HR>
103<DL>
104<DT><PRE>public class <B>ValueAggregatorReducer&lt;K1 extends <A HREF="../../../../../../org/apache/hadoop/io/WritableComparable.html" title="interface in org.apache.hadoop.io">WritableComparable</A>,V1 extends <A HREF="../../../../../../org/apache/hadoop/io/Writable.html" title="interface in org.apache.hadoop.io">Writable</A>&gt;</B><DT>extends <A HREF="../../../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorJobBase.html" title="class in org.apache.hadoop.mapred.lib.aggregate">ValueAggregatorJobBase</A>&lt;K1,V1&gt;</DL>
105</PRE>
106
107<P>
108This class implements the generic reducer of Aggregate.
109<P>
110
111<P>
112<HR>
113
114<P>
115<!-- =========== FIELD SUMMARY =========== -->
116
117<A NAME="field_summary"><!-- --></A>
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119<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
120<TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2">
121<B>Field Summary</B></FONT></TH>
122</TR>
123</TABLE>
124&nbsp;<A NAME="fields_inherited_from_class_org.apache.hadoop.mapred.lib.aggregate.ValueAggregatorJobBase"><!-- --></A>
125<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
126<TR BGCOLOR="#EEEEFF" CLASS="TableSubHeadingColor">
127<TH ALIGN="left"><B>Fields inherited from class org.apache.hadoop.mapred.lib.aggregate.<A HREF="../../../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorJobBase.html" title="class in org.apache.hadoop.mapred.lib.aggregate">ValueAggregatorJobBase</A></B></TH>
128</TR>
129<TR BGCOLOR="white" CLASS="TableRowColor">
130<TD><CODE><A HREF="../../../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorJobBase.html#aggregatorDescriptorList">aggregatorDescriptorList</A></CODE></TD>
131</TR>
132</TABLE>
133&nbsp;
134<!-- ======== CONSTRUCTOR SUMMARY ======== -->
135
136<A NAME="constructor_summary"><!-- --></A>
137<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
138<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
139<TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2">
140<B>Constructor Summary</B></FONT></TH>
141</TR>
142<TR BGCOLOR="white" CLASS="TableRowColor">
143<TD><CODE><B><A HREF="../../../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorReducer.html#ValueAggregatorReducer()">ValueAggregatorReducer</A></B>()</CODE>
144
145<BR>
146&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</TD>
147</TR>
148</TABLE>
149&nbsp;
150<!-- ========== METHOD SUMMARY =========== -->
151
152<A NAME="method_summary"><!-- --></A>
153<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
154<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
155<TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2">
156<B>Method Summary</B></FONT></TH>
157</TR>
158<TR BGCOLOR="white" CLASS="TableRowColor">
159<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
160<CODE>&nbsp;void</CODE></FONT></TD>
161<TD><CODE><B><A HREF="../../../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorReducer.html#map(K1, V1, org.apache.hadoop.mapred.OutputCollector, org.apache.hadoop.mapred.Reporter)">map</A></B>(<A HREF="../../../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorReducer.html" title="type parameter in ValueAggregatorReducer">K1</A>&nbsp;arg0,
162    <A HREF="../../../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorReducer.html" title="type parameter in ValueAggregatorReducer">V1</A>&nbsp;arg1,
163    <A HREF="../../../../../../org/apache/hadoop/mapred/OutputCollector.html" title="interface in org.apache.hadoop.mapred">OutputCollector</A>&lt;<A HREF="../../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</A>,<A HREF="../../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</A>&gt;&nbsp;arg2,
164    <A HREF="../../../../../../org/apache/hadoop/mapred/Reporter.html" title="interface in org.apache.hadoop.mapred">Reporter</A>&nbsp;arg3)</CODE>
165
166<BR>
167&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Do nothing.</TD>
168</TR>
169<TR BGCOLOR="white" CLASS="TableRowColor">
170<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
171<CODE>&nbsp;void</CODE></FONT></TD>
172<TD><CODE><B><A HREF="../../../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorReducer.html#reduce(org.apache.hadoop.io.Text, java.util.Iterator, org.apache.hadoop.mapred.OutputCollector, org.apache.hadoop.mapred.Reporter)">reduce</A></B>(<A HREF="../../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</A>&nbsp;key,
173       <A HREF="http://java.sun.com/javase/6/docs/api/java/util/Iterator.html?is-external=true" title="class or interface in java.util">Iterator</A>&lt;<A HREF="../../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</A>&gt;&nbsp;values,
174       <A HREF="../../../../../../org/apache/hadoop/mapred/OutputCollector.html" title="interface in org.apache.hadoop.mapred">OutputCollector</A>&lt;<A HREF="../../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</A>,<A HREF="../../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</A>&gt;&nbsp;output,
175       <A HREF="../../../../../../org/apache/hadoop/mapred/Reporter.html" title="interface in org.apache.hadoop.mapred">Reporter</A>&nbsp;reporter)</CODE>
176
177<BR>
178&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<i>Reduces</i> values for a given key.</TD>
179</TR>
180</TABLE>
181&nbsp;<A NAME="methods_inherited_from_class_org.apache.hadoop.mapred.lib.aggregate.ValueAggregatorJobBase"><!-- --></A>
182<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
183<TR BGCOLOR="#EEEEFF" CLASS="TableSubHeadingColor">
184<TH ALIGN="left"><B>Methods inherited from class org.apache.hadoop.mapred.lib.aggregate.<A HREF="../../../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorJobBase.html" title="class in org.apache.hadoop.mapred.lib.aggregate">ValueAggregatorJobBase</A></B></TH>
185</TR>
186<TR BGCOLOR="white" CLASS="TableRowColor">
187<TD><CODE><A HREF="../../../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorJobBase.html#close()">close</A>, <A HREF="../../../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorJobBase.html#configure(org.apache.hadoop.mapred.JobConf)">configure</A>, <A HREF="../../../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorJobBase.html#logSpec()">logSpec</A></CODE></TD>
188</TR>
189</TABLE>
190&nbsp;<A NAME="methods_inherited_from_class_java.lang.Object"><!-- --></A>
191<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
192<TR BGCOLOR="#EEEEFF" CLASS="TableSubHeadingColor">
193<TH ALIGN="left"><B>Methods inherited from class java.lang.<A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">Object</A></B></TH>
194</TR>
195<TR BGCOLOR="white" CLASS="TableRowColor">
196<TD><CODE><A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#clone()" title="class or interface in java.lang">clone</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#equals(java.lang.Object)" title="class or interface in java.lang">equals</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#finalize()" title="class or interface in java.lang">finalize</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#getClass()" title="class or interface in java.lang">getClass</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#hashCode()" title="class or interface in java.lang">hashCode</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#notify()" title="class or interface in java.lang">notify</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#notifyAll()" title="class or interface in java.lang">notifyAll</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#toString()" title="class or interface in java.lang">toString</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#wait()" title="class or interface in java.lang">wait</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#wait(long)" title="class or interface in java.lang">wait</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#wait(long, int)" title="class or interface in java.lang">wait</A></CODE></TD>
197</TR>
198</TABLE>
199&nbsp;
200<P>
201
202<!-- ========= CONSTRUCTOR DETAIL ======== -->
203
204<A NAME="constructor_detail"><!-- --></A>
205<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
206<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
207<TH ALIGN="left" COLSPAN="1"><FONT SIZE="+2">
208<B>Constructor Detail</B></FONT></TH>
209</TR>
210</TABLE>
211
212<A NAME="ValueAggregatorReducer()"><!-- --></A><H3>
213ValueAggregatorReducer</H3>
214<PRE>
215public <B>ValueAggregatorReducer</B>()</PRE>
216<DL>
217</DL>
218
219<!-- ============ METHOD DETAIL ========== -->
220
221<A NAME="method_detail"><!-- --></A>
222<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
223<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
224<TH ALIGN="left" COLSPAN="1"><FONT SIZE="+2">
225<B>Method Detail</B></FONT></TH>
226</TR>
227</TABLE>
228
229<A NAME="reduce(org.apache.hadoop.io.Text, java.util.Iterator, org.apache.hadoop.mapred.OutputCollector, org.apache.hadoop.mapred.Reporter)"><!-- --></A><H3>
230reduce</H3>
231<PRE>
232public void <B>reduce</B>(<A HREF="../../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</A>&nbsp;key,
233                   <A HREF="http://java.sun.com/javase/6/docs/api/java/util/Iterator.html?is-external=true" title="class or interface in java.util">Iterator</A>&lt;<A HREF="../../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</A>&gt;&nbsp;values,
234                   <A HREF="../../../../../../org/apache/hadoop/mapred/OutputCollector.html" title="interface in org.apache.hadoop.mapred">OutputCollector</A>&lt;<A HREF="../../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</A>,<A HREF="../../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</A>&gt;&nbsp;output,
235                   <A HREF="../../../../../../org/apache/hadoop/mapred/Reporter.html" title="interface in org.apache.hadoop.mapred">Reporter</A>&nbsp;reporter)
236            throws <A HREF="http://java.sun.com/javase/6/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</A></PRE>
237<DL>
238<DD><B>Description copied from interface: <CODE><A HREF="../../../../../../org/apache/hadoop/mapred/Reducer.html#reduce(K2, java.util.Iterator, org.apache.hadoop.mapred.OutputCollector, org.apache.hadoop.mapred.Reporter)">Reducer</A></CODE></B></DD>
239<DD><i>Reduces</i> values for a given key. 
240 
241 <p>The framework calls this method for each
242 <code>&lt;key, (list of values)></code> pair in the grouped inputs.
243 Output values must be of the same type as input values.  Input keys must
244 not be altered. The framework will <b>reuse</b> the key and value objects
245 that are passed into the reduce, therefore the application should clone
246 the objects they want to keep a copy of. In many cases, all values are
247 combined into zero or one value.
248 </p>
249   
250 <p>Output pairs are collected with calls to 
251 <A HREF="../../../../../../org/apache/hadoop/mapred/OutputCollector.html#collect(K, V)"><CODE>OutputCollector.collect(Object,Object)</CODE></A>.</p>
252
253 <p>Applications can use the <A HREF="../../../../../../org/apache/hadoop/mapred/Reporter.html" title="interface in org.apache.hadoop.mapred"><CODE>Reporter</CODE></A> provided to report progress
254 or just indicate that they are alive. In scenarios where the application
255 takes an insignificant amount of time to process individual key/value
256 pairs, this is crucial since the framework might assume that the task has
257 timed-out and kill that task. The other way of avoiding this is to set
258 <a href="../../../../../../../mapred-default.html#mapred.task.timeout">
259 mapred.task.timeout</a> to a high-enough value (or even zero for no
260 time-outs).</p>
261<P>
262<DD><DL>
263<DT><B>Parameters:</B><DD><CODE>key</CODE> - the key is expected to be a Text object, whose prefix indicates
264          the type of aggregation to aggregate the values. In effect, data
265          driven computing is achieved. It is assumed that each aggregator's
266          getReport method emits appropriate output for the aggregator. This
267          may be further customiized.<DD><CODE>values</CODE> - the list of values to reduce.<DD><CODE>output</CODE> - to collect keys and combined values.<DD><CODE>reporter</CODE> - facility to report progress.
268<DT><B>Throws:</B>
269<DD><CODE><A HREF="http://java.sun.com/javase/6/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</A></CODE></DL>
270</DD>
271</DL>
272<HR>
273
274<A NAME="map(org.apache.hadoop.io.WritableComparable,org.apache.hadoop.io.Writable,org.apache.hadoop.mapred.OutputCollector,org.apache.hadoop.mapred.Reporter)"><!-- --></A><A NAME="map(K1, V1, org.apache.hadoop.mapred.OutputCollector, org.apache.hadoop.mapred.Reporter)"><!-- --></A><H3>
275map</H3>
276<PRE>
277public void <B>map</B>(<A HREF="../../../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorReducer.html" title="type parameter in ValueAggregatorReducer">K1</A>&nbsp;arg0,
278                <A HREF="../../../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorReducer.html" title="type parameter in ValueAggregatorReducer">V1</A>&nbsp;arg1,
279                <A HREF="../../../../../../org/apache/hadoop/mapred/OutputCollector.html" title="interface in org.apache.hadoop.mapred">OutputCollector</A>&lt;<A HREF="../../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</A>,<A HREF="../../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</A>&gt;&nbsp;arg2,
280                <A HREF="../../../../../../org/apache/hadoop/mapred/Reporter.html" title="interface in org.apache.hadoop.mapred">Reporter</A>&nbsp;arg3)
281         throws <A HREF="http://java.sun.com/javase/6/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</A></PRE>
282<DL>
283<DD>Do nothing. Should not be called
284<P>
285<DD><DL>
286<DT><B>Parameters:</B><DD><CODE>arg0</CODE> - the input key.<DD><CODE>arg1</CODE> - the input value.<DD><CODE>arg2</CODE> - collects mapped keys and values.<DD><CODE>arg3</CODE> - facility to report progress.
287<DT><B>Throws:</B>
288<DD><CODE><A HREF="http://java.sun.com/javase/6/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</A></CODE></DL>
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