MapReduce Concept

MapReduce is natively Java, allowed to interface with Python under Streaming

• Like dictionary in data structure

  
  
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• Shuffle Keys and Sort Values

  
  
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• Reducer

  
  
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• So overall operation is like:

  
  
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• Handle of failure

  
  
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MapReduce Coding

• Problem:

  
  
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• Map Function:

def mapper_get_ratings(self, _, line):
    (userID, movieID,rating,Timestamp)=line.split('\t')
     yield rating,1

• Reduce Funtion:

def reducer_count_ratings(self, key, values):
    yield key, sum(values)

• After putting them together:

  
  
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Installation & Preparation

• After log into the command line interface:

  
  
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• Run locally:

python RatingsBreakdown.py u.data

• Run with Hadoop:

python RatingsBreakdown.py -r hadoop --hadoop-streaming-jar /usr/hdp/current/hadoop-mapreduce-client/hadoop-streaming.jar u.data

• Result should be :

  
  
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• Plus, codes for more complex problems (sorted for movie numbers):

  
  
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