Hadoop HelloWord Examples- 求平均数
- - CSDN博客云计算推荐文章 另外一个hadoop的入门demo,求平均数. 是对WordCount这个demo的一个小小的修改. 输入一堆成绩单(人名,成绩),然后求每个人成绩平均数,比如:. 求a,b,c这三个人的平均分. 解决思路很简单,在map阶段key是名字,value是成绩,直接output. reduce阶段得到了map输出的key名字,values是该名字对应的一系列的成绩,那么对其求平均数即可.
另外一个hadoop的入门demo,求平均数。是对WordCount这个demo的一个小小的修改。输入一堆成绩单(人名,成绩),然后求每个人成绩平均数,比如:
// subject1.txt
a 90
b 80
c 70
// subject2.txt
a 100
b 90
c 80
求a,b,c这三个人的平均分。解决思路很简单,在map阶段key是名字,value是成绩,直接output。reduce阶段得到了map输出的key名字,values是该名字对应的一系列的成绩,那么对其求平均数即可。
这里我们实现了两个版本的代码,分别用TextInputFormat和 KeyValueTextInputFormat来作为输入格式。
TextInputFormat版本:
import java.util.*; import java.io.*; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.fs.Path; import org.apache.hadoop.io.Text; import org.apache.hadoop.io.IntWritable; import org.apache.hadoop.mapreduce.Mapper; import org.apache.hadoop.mapreduce.Reducer; import org.apache.hadoop.mapreduce.Job; import org.apache.hadoop.mapreduce.lib.input.FileInputFormat; import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat; public class AveScore { public static class AveMapper extends Mapper<Object, Text, Text, IntWritable> { @Override public void map(Object key, Text value, Context context) throws IOException, InterruptedException { String line = value.toString(); String[] strs = line.split(" "); String name = strs[0]; int score = Integer.parseInt(strs[1]); context.write(new Text(name), new IntWritable(score)); } } public static class AveReducer extends Reducer<Text, IntWritable, Text, IntWritable> { @Override public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException { int sum = 0; int count = 0; for(IntWritable val : values) { sum += val.get(); count++; } int aveScore = sum / count; context.write(key, new IntWritable(aveScore)); } } public static void main(String[] args) throws Exception { Configuration conf = new Configuration(); Job job = new Job(conf,"AverageScore"); job.setJarByClass(AveScore.class); job.setMapperClass(AveMapper.class); job.setReducerClass(AveReducer.class); job.setOutputKeyClass(Text.class); job.setOutputValueClass(IntWritable.class); FileInputFormat.addInputPath(job, new Path(args[0])); FileOutputFormat.setOutputPath(job, new Path(args[1])); System.exit( job.waitForCompletion(true) ? 0 : 1); } }
KeyValueTextInputFormat版本;
import java.util.*; import java.io.*; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.fs.Path; import org.apache.hadoop.io.Text; import org.apache.hadoop.io.IntWritable; import org.apache.hadoop.mapreduce.Mapper; import org.apache.hadoop.mapreduce.Reducer; import org.apache.hadoop.mapreduce.Job; import org.apache.hadoop.mapreduce.lib.input.FileInputFormat; import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat; import org.apache.hadoop.mapreduce.lib.input.KeyValueTextInputFormat; import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat; public class AveScore_KeyValue { public static class AveMapper extends Mapper<Text, Text, Text, IntWritable> { @Override public void map(Text key, Text value, Context context) throws IOException, InterruptedException { int score = Integer.parseInt(value.toString()); context.write(key, new IntWritable(score) ); } } public static class AveReducer extends Reducer<Text, IntWritable, Text, IntWritable> { @Override public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException { int sum = 0; int count = 0; for(IntWritable val : values) { sum += val.get(); count++; } int aveScore = sum / count; context.write(key, new IntWritable(aveScore)); } } public static void main(String[] args) throws Exception { Configuration conf = new Configuration(); conf.set("mapreduce.input.keyvaluelinerecordreader.key.value.separator", " "); Job job = new Job(conf,"AverageScore"); job.setJarByClass(AveScore_KeyValue.class); job.setMapperClass(AveMapper.class); job.setReducerClass(AveReducer.class); job.setOutputKeyClass(Text.class); job.setOutputValueClass(IntWritable.class); job.setInputFormatClass(KeyValueTextInputFormat.class); job.setOutputFormatClass(TextOutputFormat.class) ; FileInputFormat.addInputPath(job, new Path(args[0])); FileOutputFormat.setOutputPath(job, new Path(args[1])); System.exit( job.waitForCompletion(true) ? 0 : 1); } }
输出结果为:
a 95
b 85
c 75