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hadoopmapreducehadoop2

How to sort data in descending order in map reduce?

My reducer gives this o/p 

Country-Year,Medals
India-2008,60
United States-2008,1237
Zimbabwe-2008, 2
Namibia-2009,22
China-2009,43
United States-2009,54

And i want this, sorting should happen based on medals and top three should be shown.

Country-Year,Medals
United States-2008,1237
India-2008,60
United States-2009,54

Someone suggested me to do this sorting in custom recordreader(understood that it is used in mapper part) and i browsed through some resources but couldn't find much on sorting. Please share any ideas or link to resources. Advance thanks !

Solution

  • You can implement Map Reduce Top K Design pattern to achieve your objective.

    Top K Design pattern will sort your records on values and picks the top k records.

    You can go through this link for implementing Top K Design pattern on your data.