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MapReduce 基本指令操作
Basic Commands of Hadoop MapReduce

}}} [[PageOutline]] {{{ #!text 請先連線至 nodeN.3du.me , N 為您的報名編號 }}} == Sample 1 : 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 fs -put ${HOME}/hadoop/conf lab11_input ~$ hadoop fs -rmr lab11_out2 ~$ hadoop jar ${HOME}/hadoop/hadoop-examples-*.jar wordcount lab11_input lab11_out2 }}} * 檢查輸出結果的方法同之前方法[[BR]]Let's check the computed result of '''wordcount''' from HDFS : {{{ ~$ hadoop fs -ls lab11_out2 ~$ hadoop fs -cat lab11_out2/part-r-00000 }}} * 結果如下[[BR]]You should see results like this: {{{ "". 4 "*" 9 "127.0.0.1" 3 "AS 2 "License"); 2 "_logs/history/" 1 "alice,bob 9 ( ... skip ... ) }}} == Sample 2: 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 -ls lab11_input ~$ hadoop jar ${HOME}/hadoop/hadoop-examples-*.jar grep lab11_input lab11_out3 'dfs[a-z.]+' }}} * 運作的畫面如下:[[BR]]You should see procedure like this: {{{ 11/04/19 10:00:20 INFO mapred.FileInputFormat: Total input paths to process : 25 11/04/19 10:00:20 INFO mapred.JobClient: Running job: job_201104120101_0645 11/04/19 10:00:21 INFO mapred.JobClient: map 0% reduce 0% ( ... skip ... ) }}} * 接著查看結果[[BR]]Let's check the computed result of '''grep''' from HDFS : {{{ ~$ hadoop fs -ls lab11_out3 ~$ hadoop fs -cat lab11_out3/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 ... ) }}} == 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]