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courses:mapreduce-tutorial:step-29 [2012/02/05 19:04]
straka 		courses:mapreduce-tutorial:step-29 [2012/02/05 19:14] (current)
straka
Line 82: Line 82:
 job.setGroupingComparatorClass(IntPair.FirstOnlyComparator.class); job.setGroupingComparatorClass(IntPair.FirstOnlyComparator.class);
 </code> </code>
 +
 +====== Exercise ======
 +
 +Improve the [[.:step-28#exercise-1|inverted index exercise]] from the previous step to create for each word a //sorted// list of ''DocWithOccurrences<Text>''.
 +
 +Use the same approach as with the ''IntPair'' -- create a type ''TextPair'', which stores two values of type ''Text'' and let the mapper create ''(TextPair, DocWithOccurrences<Text>'' pairs, where the ''TextPair'' contains the word and then the document. Provide a ''FirstOnlyComparator'' which compares two ''TextPair''s using only the word (hint: use [[http://hadoop.apache.org/common/docs/r1.0.0/api/org/apache/hadoop/io/Text.Comparator.html#compare(byte[],%20int,%20int,%20byte[],%20int,%20int)|Text.Comparator.compare]] when defining the byte version ''FirstOnlyComparator.compare'') and use it as a grouping comparator.
  
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