Time for action – WordCount, the Hello World of MapReduce

Many applications, over time, acquire a canonical example that no beginner's guide should be without. For Hadoop, this is WordCount – an example bundled with Hadoop that counts the frequency of words in an input text file.

1. First execute the following commands:

   $ hadoop dfs -mkdir data
   $ hadoop dfs -cp test.txt data
   $ hadoop dfs -ls data
   Found 1 items
   -rw-r--r--   1 hadoop supergroup         16 2012-10-26 23:20 /user/hadoop/data/test.txt
   

2. Now execute these commands:

   $ Hadoop Hadoop/hadoop-examples-1.0.4.jar  wordcount data out
   12/10/26 23:22:49 INFO input.FileInputFormat: Total input paths to process : 1
   12/10/26 23:22:50 INFO mapred.JobClient: Running job: job_201210262315_0002
   12/10/26 23:22:51 INFO mapred.JobClient:  map 0% reduce 0%
   12/10/26 23:23:03 INFO mapred.JobClient:  map 100% reduce 0%
   12/10/26 23:23:15 INFO mapred.JobClient:  map 100% reduce 100%
   12/10/26 23:23:17 INFO mapred.JobClient: Job complete: job_201210262315_0002...