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courses:mapreduce-tutorial:step-5 [2012/01/28 12:52]
majlis Added links to previous and next chapter. 		courses:mapreduce-tutorial:step-5 [2012/01/29 20:21]
straka
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 The interesting part of a Hadoop job is the //reducer// -- after all mappers produce the (key, value) pairs, for every unique key and all its values a ''reduce'' function is called. The ''reduce'' function can output (key, value) pairs, which are written to disk. The interesting part of a Hadoop job is the //reducer// -- after all mappers produce the (key, value) pairs, for every unique key and all its values a ''reduce'' function is called. The ''reduce'' function can output (key, value) pairs, which are written to disk.
  
-The ''reduce'' is similar to ''map'', but instead of one value it gets an iterator, which enumerates all values associated with the key:+The ''reduce'' is similar to ''map'', but instead of one value it gets an iterator (instance of ''Hadoop::Runner::ValueIterator''), which enumerates all values associated with the key:
  
 <file perl> <file perl>

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