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courses:mapreduce-tutorial:step-29 [2012/01/31 13:12]
straka 		courses:mapreduce-tutorial:step-29 [2012/02/05 18:23]
straka
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 ====== MapReduce Tutorial : Custom sorting and grouping comparators. ====== ====== MapReduce Tutorial : Custom sorting and grouping comparators. ======
  
 +====== Sorting comparator ======
 +
 +The keys are sorted before processed by a reducer, using a
 +[[http://hadoop.apache.org/common/docs/r1.0.0/api/org/apache/hadoop/io/RawComparator.html|Raw comparator]].
 +
 +====== Grouping comparator ======
 +
 +In a reduce, it is guaranteed that keys are processed in ascending order. Sometimes it would be useful if the //values associated with one key// could also be processed in ascending order.
  
 ---- ----
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 <table style="width:100%"> <table style="width:100%">
 <tr> <tr>
-<td style="text-align:left; width: 33%; "></html>[[step-28|Step 28]]: Running multiple Hadoop jobs in one source file.<html></td>+<td style="text-align:left; width: 33%; "></html>[[step-28|Step 28]]: Custom data types.<html></td>
 <td style="text-align:center; width: 33%; "></html>[[.|Overview]]<html></td> <td style="text-align:center; width: 33%; "></html>[[.|Overview]]<html></td>
 <td style="text-align:right; width: 33%; "></html>[[step-30|Step 30]]: Custom input formats.<html></td> <td style="text-align:right; width: 33%; "></html>[[step-30|Step 30]]: Custom input formats.<html></td>
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 </table> </table>
 </html> </html>
 +

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