MapReduce数据分析（4）最大值

四：MapReduce第四讲：Max（最大值）

最大值的话小编没有什么可以说的，我相信大家都明白，这次我就直接上案列和代码了。

数据如下：

案列：编写MapReduce代码获得每年的最高气温。

代码：

package demo;

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
//2014010114

public class MaxTmp {
	public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
		Configuration conf=new Configuration();
		Job job = Job.getInstance(conf);
		job.setJarByClass(demo.class);
		job.setMapperClass(MMapper.class);
		job.setReducerClass(MReduce.class);
		job.setMapOutputKeyClass(Text.class);
		job.setMapOutputValueClass(IntWritable.class);
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(LongWritable.class);
		FileInputFormat.setInputPaths(job, new Path(args[0]));
		FileOutputFormat.setOutputPath(job, new Path(args[1]));
		job.waitForCompletion(true);


	}
	
	public static class MMapper extends Mapper<LongWritable, Text, Text, IntWritable>{


		protected void map(LongWritable key, Text value, Context context)
				throws IOException, InterruptedException {
			//转换数据类型
			String line = value.toString();
			//截取数据中的0-6位。
			String year = line.substring(0,6);
			//转换int类型并截取数据中的8-10位
			int tmp = Integer.parseInt(line.substring(8,10));
			//直接写入
			context.write(new Text(year), new IntWritable(tmp));
			//201401    14
		}

	}
	public static class MReduce extends Reducer<Text, IntWritable, Text, IntWritable>{
		private IntWritable v = new IntWritable();
		
		protected void reduce(Text key, Iterable<IntWritable> value,
				Context context) throws IOException, InterruptedException {
			//			 14
	
			int maxv = Integer.MIN_VALUE;
			
			for (IntWritable v : value) {
			
				maxv=Math.max(maxv, v.get());
			
			}
			v.set(maxv);
		
			context.write(key, v);
			
		}

	}


}

运行结果：

下面我附上全部数据：
2014010114
2014010216
2014010317
2014010410
2014010506
2012010609
2012010732
2012010812
2012010919
2012011023
2001010116
2001010212
2001010310
2001010411
2001010529
2013010619
2013010722
2013010812
2013010929
2013011023
2008010105
2008010216
2008010337
2008010414
2008010516
2007010619
2007010712
2007010812
2007010999
2007011023
2010010114
2010010216
2010010317
2010010410
2010010506
2015010649
2015010722
2015010812
2015010999
2015011023

本次教程就到此结束了，博主会把关于MapReduce数据分析的各种操作讲解给大家听。有什么不懂的下方评论，博主看到都会去解答的。还有不要忘了多多支持博主呦，你们的支持就是我的动力。