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91org.apache.hadoop.mapred</FONT>
92<BR>
93Interface Mapper&lt;K1,V1,K2,V2&gt;</H2>
94<DL>
95<DT><B>All Superinterfaces:</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></DD>
96</DL>
97<DL>
98<DT><B>All Known Subinterfaces:</B> <DD><A HREF="../../../../org/apache/hadoop/contrib/index/mapred/ILocalAnalysis.html" title="interface in org.apache.hadoop.contrib.index.mapred">ILocalAnalysis</A>&lt;K,V&gt;</DD>
99</DL>
100<DL>
101<DT><B>All Known Implementing Classes:</B> <DD><A HREF="../../../../org/apache/hadoop/mapred/lib/ChainMapper.html" title="class in org.apache.hadoop.mapred.lib">ChainMapper</A>, <A HREF="../../../../org/apache/hadoop/contrib/utils/join/DataJoinMapperBase.html" title="class in org.apache.hadoop.contrib.utils.join">DataJoinMapperBase</A>, <A HREF="../../../../org/apache/hadoop/contrib/utils/join/DataJoinReducerBase.html" title="class in org.apache.hadoop.contrib.utils.join">DataJoinReducerBase</A>, <A HREF="../../../../org/apache/hadoop/mapred/lib/DelegatingMapper.html" title="class in org.apache.hadoop.mapred.lib">DelegatingMapper</A>, <A HREF="../../../../org/apache/hadoop/examples/dancing/DistributedPentomino.PentMap.html" title="class in org.apache.hadoop.examples.dancing">DistributedPentomino.PentMap</A>, <A HREF="../../../../org/apache/hadoop/mapred/lib/FieldSelectionMapReduce.html" title="class in org.apache.hadoop.mapred.lib">FieldSelectionMapReduce</A>, <A HREF="../../../../org/apache/hadoop/contrib/index/example/IdentityLocalAnalysis.html" title="class in org.apache.hadoop.contrib.index.example">IdentityLocalAnalysis</A>, <A HREF="../../../../org/apache/hadoop/mapred/lib/IdentityMapper.html" title="class in org.apache.hadoop.mapred.lib">IdentityMapper</A>, <A HREF="../../../../org/apache/hadoop/contrib/index/mapred/IndexUpdateMapper.html" title="class in org.apache.hadoop.contrib.index.mapred">IndexUpdateMapper</A>, <A HREF="../../../../org/apache/hadoop/mapred/lib/InverseMapper.html" title="class in org.apache.hadoop.mapred.lib">InverseMapper</A>, <A HREF="../../../../org/apache/hadoop/contrib/utils/join/JobBase.html" title="class in org.apache.hadoop.contrib.utils.join">JobBase</A>, <A HREF="../../../../org/apache/hadoop/contrib/index/example/LineDocLocalAnalysis.html" title="class in org.apache.hadoop.contrib.index.example">LineDocLocalAnalysis</A>, <A HREF="../../../../org/apache/hadoop/examples/MultiFileWordCount.MapClass.html" title="class in org.apache.hadoop.examples">MultiFileWordCount.MapClass</A>, <A HREF="../../../../org/apache/hadoop/examples/PiEstimator.PiMapper.html" title="class in org.apache.hadoop.examples">PiEstimator.PiMapper</A>, <A HREF="../../../../org/apache/hadoop/streaming/PipeMapper.html" title="class in org.apache.hadoop.streaming">PipeMapper</A>, <A HREF="../../../../org/apache/hadoop/mapred/lib/RegexMapper.html" title="class in org.apache.hadoop.mapred.lib">RegexMapper</A>, <A HREF="../../../../org/apache/hadoop/examples/SleepJob.html" title="class in org.apache.hadoop.examples">SleepJob</A>, <A HREF="../../../../org/apache/hadoop/examples/terasort/TeraGen.SortGenMapper.html" title="class in org.apache.hadoop.examples.terasort">TeraGen.SortGenMapper</A>, <A HREF="../../../../org/apache/hadoop/mapred/lib/TokenCountMapper.html" title="class in org.apache.hadoop.mapred.lib">TokenCountMapper</A>, <A HREF="../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorCombiner.html" title="class in org.apache.hadoop.mapred.lib.aggregate">ValueAggregatorCombiner</A>, <A HREF="../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorJobBase.html" title="class in org.apache.hadoop.mapred.lib.aggregate">ValueAggregatorJobBase</A>, <A HREF="../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorMapper.html" title="class in org.apache.hadoop.mapred.lib.aggregate">ValueAggregatorMapper</A>, <A HREF="../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorReducer.html" title="class in org.apache.hadoop.mapred.lib.aggregate">ValueAggregatorReducer</A></DD>
102</DL>
103<HR>
104<B>Deprecated.</B>&nbsp;<I>Use <A HREF="../../../../org/apache/hadoop/mapreduce/Mapper.html" title="class in org.apache.hadoop.mapreduce"><CODE>Mapper</CODE></A> instead.</I>
105<P>
106<DL>
107<DT><PRE><FONT SIZE="-1"><A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Deprecated.html?is-external=true" title="class or interface in java.lang">@Deprecated</A>
108</FONT>public interface <B>Mapper&lt;K1,V1,K2,V2&gt;</B><DT>extends <A HREF="../../../../org/apache/hadoop/mapred/JobConfigurable.html" title="interface in org.apache.hadoop.mapred">JobConfigurable</A>, <A HREF="../../../../org/apache/hadoop/io/Closeable.html" title="interface in org.apache.hadoop.io">Closeable</A></DL>
109</PRE>
110
111<P>
112Maps input key/value pairs to a set of intermediate key/value pairs. 
113 
114 <p>Maps are the individual tasks which transform input records into a
115 intermediate records. The transformed intermediate records need not be of
116 the same type as the input records. A given input pair may map to zero or
117 many output pairs.</p> 
118 
119 <p>The Hadoop Map-Reduce framework spawns one map task for each
120 <A HREF="../../../../org/apache/hadoop/mapred/InputSplit.html" title="interface in org.apache.hadoop.mapred"><CODE>InputSplit</CODE></A> generated by the <A HREF="../../../../org/apache/hadoop/mapred/InputFormat.html" title="interface in org.apache.hadoop.mapred"><CODE>InputFormat</CODE></A> for the job.
121 <code>Mapper</code> implementations can access the <A HREF="../../../../org/apache/hadoop/mapred/JobConf.html" title="class in org.apache.hadoop.mapred"><CODE>JobConf</CODE></A> for the
122 job via the <A HREF="../../../../org/apache/hadoop/mapred/JobConfigurable.html#configure(org.apache.hadoop.mapred.JobConf)"><CODE>JobConfigurable.configure(JobConf)</CODE></A> and initialize
123 themselves. Similarly they can use the <A HREF="http://java.sun.com/javase/6/docs/api/java/io/Closeable.html?is-external=true#close()" title="class or interface in java.io"><CODE>Closeable.close()</CODE></A> method for
124 de-initialization.</p>
125 
126 <p>The framework then calls
127 <A HREF="../../../../org/apache/hadoop/mapred/Mapper.html#map(K1, V1, org.apache.hadoop.mapred.OutputCollector, org.apache.hadoop.mapred.Reporter)"><CODE>map(Object, Object, OutputCollector, Reporter)</CODE></A> 
128 for each key/value pair in the <code>InputSplit</code> for that task.</p>
129 
130 <p>All intermediate values associated with a given output key are
131 subsequently grouped by the framework, and passed to a <A HREF="../../../../org/apache/hadoop/mapred/Reducer.html" title="interface in org.apache.hadoop.mapred"><CODE>Reducer</CODE></A> to 
132 determine the final output. Users can control the grouping by specifying
133 a <code>Comparator</code> via
134 <A HREF="../../../../org/apache/hadoop/mapred/JobConf.html#setOutputKeyComparatorClass(java.lang.Class)"><CODE>JobConf.setOutputKeyComparatorClass(Class)</CODE></A>.</p>
135
136 <p>The grouped <code>Mapper</code> outputs are partitioned per
137 <code>Reducer</code>. Users can control which keys (and hence records) go to
138 which <code>Reducer</code> by implementing a custom <A HREF="../../../../org/apache/hadoop/mapred/Partitioner.html" title="interface in org.apache.hadoop.mapred"><CODE>Partitioner</CODE></A>.
139 
140 <p>Users can optionally specify a <code>combiner</code>, via
141 <A HREF="../../../../org/apache/hadoop/mapred/JobConf.html#setCombinerClass(java.lang.Class)"><CODE>JobConf.setCombinerClass(Class)</CODE></A>, to perform local aggregation of the
142 intermediate outputs, which helps to cut down the amount of data transferred
143 from the <code>Mapper</code> to the <code>Reducer</code>.
144 
145 <p>The intermediate, grouped outputs are always stored in
146 <A HREF="../../../../org/apache/hadoop/io/SequenceFile.html" title="class in org.apache.hadoop.io"><CODE>SequenceFile</CODE></A>s. Applications can specify if and how the intermediate
147 outputs are to be compressed and which <A HREF="../../../../org/apache/hadoop/io/compress/CompressionCodec.html" title="interface in org.apache.hadoop.io.compress"><CODE>CompressionCodec</CODE></A>s are to be
148 used via the <code>JobConf</code>.</p>
149 
150 <p>If the job has
151 <a href="../../../../org/apache/hadoop/mapred/JobConf.html#ReducerNone">zero
152 reduces</a> then the output of the <code>Mapper</code> is directly written
153 to the <A HREF="../../../../org/apache/hadoop/fs/FileSystem.html" title="class in org.apache.hadoop.fs"><CODE>FileSystem</CODE></A> without grouping by keys.</p>
154 
155 <p>Example:</p>
156 <p><blockquote><pre>
157     public class MyMapper&lt;K extends WritableComparable, V extends Writable&gt; 
158     extends MapReduceBase implements Mapper&lt;K, V, K, V&gt; {
159     
160       static enum MyCounters { NUM_RECORDS }
161       
162       private String mapTaskId;
163       private String inputFile;
164       private int noRecords = 0;
165       
166       public void configure(JobConf job) {
167         mapTaskId = job.get("mapred.task.id");
168         inputFile = job.get("map.input.file");
169       }
170       
171       public void map(K key, V val,
172                       OutputCollector&lt;K, V&gt; output, Reporter reporter)
173       throws IOException {
174         // Process the &lt;key, value&gt; pair (assume this takes a while)
175         // ...
176         // ...
177         
178         // Let the framework know that we are alive, and kicking!
179         // reporter.progress();
180         
181         // Process some more
182         // ...
183         // ...
184         
185         // Increment the no. of &lt;key, value&gt; pairs processed
186         ++noRecords;
187
188         // Increment counters
189         reporter.incrCounter(NUM_RECORDS, 1);
190       
191         // Every 100 records update application-level status
192         if ((noRecords%100) == 0) {
193           reporter.setStatus(mapTaskId + " processed " + noRecords +
194                              " from input-file: " + inputFile);
195         }
196         
197         // Output the result
198         output.collect(key, val);
199       }
200     }
201 </pre></blockquote></p>
202
203 <p>Applications may write a custom <A HREF="../../../../org/apache/hadoop/mapred/MapRunnable.html" title="interface in org.apache.hadoop.mapred"><CODE>MapRunnable</CODE></A> to exert greater
204 control on map processing e.g. multi-threaded <code>Mapper</code>s etc.</p>
205<P>
206
207<P>
208<DL>
209<DT><B>See Also:</B><DD><A HREF="../../../../org/apache/hadoop/mapred/JobConf.html" title="class in org.apache.hadoop.mapred"><CODE>JobConf</CODE></A>,
210<A HREF="../../../../org/apache/hadoop/mapred/InputFormat.html" title="interface in org.apache.hadoop.mapred"><CODE>InputFormat</CODE></A>,
211<A HREF="../../../../org/apache/hadoop/mapred/Partitioner.html" title="interface in org.apache.hadoop.mapred"><CODE>Partitioner</CODE></A>,
212<A HREF="../../../../org/apache/hadoop/mapred/Reducer.html" title="interface in org.apache.hadoop.mapred"><CODE>Reducer</CODE></A>,
213<A HREF="../../../../org/apache/hadoop/mapred/MapReduceBase.html" title="class in org.apache.hadoop.mapred"><CODE>MapReduceBase</CODE></A>,
214<A HREF="../../../../org/apache/hadoop/mapred/MapRunnable.html" title="interface in org.apache.hadoop.mapred"><CODE>MapRunnable</CODE></A>,
215<A HREF="../../../../org/apache/hadoop/io/SequenceFile.html" title="class in org.apache.hadoop.io"><CODE>SequenceFile</CODE></A></DL>
216<HR>
217
218<P>
219
220<!-- ========== METHOD SUMMARY =========== -->
221
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225<TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2">
226<B>Method Summary</B></FONT></TH>
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229<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
230<CODE>&nbsp;void</CODE></FONT></TD>
231<TD><CODE><B><A HREF="../../../../org/apache/hadoop/mapred/Mapper.html#map(K1, V1, org.apache.hadoop.mapred.OutputCollector, org.apache.hadoop.mapred.Reporter)">map</A></B>(<A HREF="../../../../org/apache/hadoop/mapred/Mapper.html" title="type parameter in Mapper">K1</A>&nbsp;key,
232    <A HREF="../../../../org/apache/hadoop/mapred/Mapper.html" title="type parameter in Mapper">V1</A>&nbsp;value,
233    <A HREF="../../../../org/apache/hadoop/mapred/OutputCollector.html" title="interface in org.apache.hadoop.mapred">OutputCollector</A>&lt;<A HREF="../../../../org/apache/hadoop/mapred/Mapper.html" title="type parameter in Mapper">K2</A>,<A HREF="../../../../org/apache/hadoop/mapred/Mapper.html" title="type parameter in Mapper">V2</A>&gt;&nbsp;output,
234    <A HREF="../../../../org/apache/hadoop/mapred/Reporter.html" title="interface in org.apache.hadoop.mapred">Reporter</A>&nbsp;reporter)</CODE>
235
236<BR>
237&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>Deprecated.</B>&nbsp;Maps a single input key/value pair into an intermediate key/value pair.</TD>
238</TR>
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243<TH ALIGN="left"><B>Methods inherited from interface org.apache.hadoop.mapred.<A HREF="../../../../org/apache/hadoop/mapred/JobConfigurable.html" title="interface in org.apache.hadoop.mapred">JobConfigurable</A></B></TH>
244</TR>
245<TR BGCOLOR="white" CLASS="TableRowColor">
246<TD><CODE><A HREF="../../../../org/apache/hadoop/mapred/JobConfigurable.html#configure(org.apache.hadoop.mapred.JobConf)">configure</A></CODE></TD>
247</TR>
248</TABLE>
249&nbsp;<A NAME="methods_inherited_from_class_java.io.Closeable"><!-- --></A>
250<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
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252<TH ALIGN="left"><B>Methods inherited from interface java.io.<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></B></TH>
253</TR>
254<TR BGCOLOR="white" CLASS="TableRowColor">
255<TD><CODE><A HREF="http://java.sun.com/javase/6/docs/api/java/io/Closeable.html?is-external=true#close()" title="class or interface in java.io">close</A></CODE></TD>
256</TR>
257</TABLE>
258&nbsp;
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266<TH ALIGN="left" COLSPAN="1"><FONT SIZE="+2">
267<B>Method Detail</B></FONT></TH>
268</TR>
269</TABLE>
270
271<A NAME="map(java.lang.Object,java.lang.Object,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>
272map</H3>
273<PRE>
274void <B>map</B>(<A HREF="../../../../org/apache/hadoop/mapred/Mapper.html" title="type parameter in Mapper">K1</A>&nbsp;key,
275         <A HREF="../../../../org/apache/hadoop/mapred/Mapper.html" title="type parameter in Mapper">V1</A>&nbsp;value,
276         <A HREF="../../../../org/apache/hadoop/mapred/OutputCollector.html" title="interface in org.apache.hadoop.mapred">OutputCollector</A>&lt;<A HREF="../../../../org/apache/hadoop/mapred/Mapper.html" title="type parameter in Mapper">K2</A>,<A HREF="../../../../org/apache/hadoop/mapred/Mapper.html" title="type parameter in Mapper">V2</A>&gt;&nbsp;output,
277         <A HREF="../../../../org/apache/hadoop/mapred/Reporter.html" title="interface in org.apache.hadoop.mapred">Reporter</A>&nbsp;reporter)
278         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>
279<DL>
280<DD><B>Deprecated.</B>&nbsp;<DD>Maps a single input key/value pair into an intermediate key/value pair.
281 
282 <p>Output pairs need not be of the same types as input pairs.  A given
283 input pair may map to zero or many output pairs.  Output pairs are
284 collected with calls to
285 <A HREF="../../../../org/apache/hadoop/mapred/OutputCollector.html#collect(K, V)"><CODE>OutputCollector.collect(Object,Object)</CODE></A>.</p>
286
287 <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
288 or just indicate that they are alive. In scenarios where the application
289 takes an insignificant amount of time to process individual key/value
290 pairs, this is crucial since the framework might assume that the task has
291 timed-out and kill that task. The other way of avoiding this is to set
292 <a href="../../../../../mapred-default.html#mapred.task.timeout">
293 mapred.task.timeout</a> to a high-enough value (or even zero for no
294 time-outs).</p>
295<P>
296<DD><DL>
297</DL>
298</DD>
299<DD><DL>
300<DT><B>Parameters:</B><DD><CODE>key</CODE> - the input key.<DD><CODE>value</CODE> - the input value.<DD><CODE>output</CODE> - collects mapped keys and values.<DD><CODE>reporter</CODE> - facility to report progress.
301<DT><B>Throws:</B>
302<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>
303</DD>
304</DL>
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