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執行 MapReduce 基本運算
Running MapReduce by Examples
}}} = Sample 1: grep = * grep 這個命令是擷取文件裡面特定的字元，在Hadoop example中此指令可以擷取文件中有此指定文字的字串，並作計數統計[[BR]]grep is a command to extract specific characters in documents. In hadoop examples, you can use this command to extract strings match the regular expression and count for matched strings. {{{ $ hadoop fs -put /etc/hadoop/conf lab5_input $ hadoop fs -ls lab5_input $ hadoop jar hadoop-examples.jar grep lab5_input lab5_out1 'dfs[a-z.]+' }}} 運作的畫面如下：[[BR]]You should see procedure like this: {{{ 11/04/19 10:00:20 INFO mapred.FileInputFormat: Total input paths to process : 25 11/04/19 10:00:20 INFO mapred.JobClient: Running job: job_201104120101_0645 11/04/19 10:00:21 INFO mapred.JobClient: map 0% reduce 0% ( ... skip ... ) }}} * 接著查看結果[[BR]]Let's check the computed result of '''grep''' from HDFS : {{{ $ hadoop fs -ls lab5_out1 Found 2 items drwx------ - hXXXX supergroup 0 2011-04-19 10:00 /user/hXXXX/lab5_out1/_logs -rw-r--r-- 2 hXXXX supergroup 1146 2011-04-19 10:00 /user/hXXXX/lab5_out1/part-00000 $ hadoop fs -cat lab5_out1/part-00000 }}} 結果如下[[BR]]You should see results like this: {{{ 4 dfs.permissions 4 dfs.replication 4 dfs.name.dir 3 dfs.namenode.decommission.interval. 3 dfs.namenode.decommission.nodes.per.interval 3 dfs. ( ... skip ... ) }}} = Sample 2 : WordCount = * 如名稱，WordCount會對所有的字作字數統計，並且從a-z作排列[[BR]]WordCount example will count each word shown in documents and sorting from a to z. {{{ ~$ hadoop jar hadoop-examples.jar wordcount lab5_input lab5_out2 }}} 檢查輸出結果的方法同之前方法[[BR]]Let's check the computed result of '''wordcount''' from HDFS : {{{ $ hadoop fs -ls lab5_out2 $ hadoop fs -cat lab5_out2/part-r-00000 }}} = More Examples = 可執行的指令一覽表：[[BR]]Here is a list of hadoop examples : || aggregatewordcount || An Aggregate based map/reduce program that counts the words in the input files. || || aggregatewordhist || An Aggregate based map/reduce program that computes the histogram of the words in the input files. || || grep || A map/reduce program that counts the matches of a regex in the input. || || join || A job that effects a join over sorted, equally partitioned datasets || || multifilewc || A job that counts words from several files. || || pentomino || A map/reduce tile laying program to find solutions to pentomino problems. || || pi || A map/reduce program that estimates Pi using monte-carlo method. || || randomtextwriter || A map/reduce program that writes 10GB of random textual data per node. || || randomwriter || A map/reduce program that writes 10GB of random data per node. || || sleep || A job that sleeps at each map and reduce task. || || sort || A map/reduce program that sorts the data written by the random writer. || || sudoku || A sudoku solver. || || wordcount || A map/reduce program that counts the words in the input files. || You could find more detail at [http://hadoop.apache.org/core/docs/current/api/org/apache/hadoop/examples/package-summary.html org.apache.hadoop.examples]