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courses:mapreduce-tutorial:step-24 [2012/01/27 23:47]
straka
courses:mapreduce-tutorial:step-24 [2012/01/27 23:57]
straka
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 We start by going through a simple Hadoop job with Mapper only. We start by going through a simple Hadoop job with Mapper only.
  
-A mapper which processes (key, value) pairs of types (Kin, Vin) and produces (key, value) pairs of types (Kout, Vout) must be a subclass of [[http://hadoop.apache.org/common/docs/r1.0.0/api/org/apache/hadoop/mapreduce/Mapper.html|Mapper<Kin, Vin, Kout, Vout>]]. In our case, the mapper is subclass of ''Mapper<Text, Text, Text, Text>''.+//mapper// which processes (key, value) pairs of types (Kin, Vin) and produces (key, value) pairs of types (Kout, Vout) must be a subclass of [[http://hadoop.apache.org/common/docs/r1.0.0/api/org/apache/hadoop/mapreduce/Mapper.html|Mapper<Kin, Vin, Kout, Vout>]]. In our case, the mapper is subclass of ''Mapper<Text, Text, Text, Text>''.
  
 The mapper must define a ''map'' method and may provide ''setup'' and ''context'' method: The mapper must define a ''map'' method and may provide ''setup'' and ''context'' method:
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 </file> </file>
  
-=== Remarks ===+==== Remarks ====
   * The filename //must// be the same as the name of the class -- this is enforced by Java compiler.   * The filename //must// be the same as the name of the class -- this is enforced by Java compiler.
   * In one class multiple jobs can be submitted, either in sequence or in parallel.   * In one class multiple jobs can be submitted, either in sequence or in parallel.

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