输入n个数，返回TOP5的数字

scala实现，以各个数字为key,""为空，按照key进行排序，取出前5个

object Top5 {
  def main(args: Array[String]): Unit = {
    val conf = new SparkConf().setMaster("")
    val sc = new SparkContext(conf)
    val one = sc.textFile("/spark/test")
    var index=0
    val text=one.filter(x=>(x.trim.length>0)&&(x.split(",").length==4)).map(_.split(",")(2).toInt).
      map(x=>(x,"")).sortByKey(false).map(x=>x._1).take(5).foreach(x=>{
      index=index+1
      println("top index:"+index+"\t"+x)
    })

  }
}

Mapreduce实现，(key,"") =>(index+"",key)

MapReduce中的IntWritable默认是按照降序排列的，要实现升序排序，自己实现MyIntWritabel

public class MyIntWritable implements WritableComparable<MyIntWritable> {
    private  Integer num;

    public MyIntWritable(Integer num){
        this.num=num;
    }

    public MyIntWritable(){}

    public void write(DataOutput output) throws IOException {
        output.writeInt(num);
    }

    public void  readFields(DataInput input) throws IOException {
        this.num=input.readInt();
    }

    public int compareTo(MyIntWritable o){
        int minux=this.num-o.num;
        return minux*(-1);
    }

    @Override
    public int hashCode() {
        return this.num.hashCode();
    }

    public String toSting(){
        return this.num+"";
    }

    public boolean equals(Object obj) {
        if (obj instanceof MyIntWritable) {
            return false;
        }
        MyIntWritable ok2 = (MyIntWritable) obj;
        return (this.num == ok2.num);
    }
}

package HadoopvsSpark;

import org.apache.hadoop.fs.FileSystem;
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;

import java.io.IOException;

/**
 * Created by Administrator on 2017/5/26.
 */
public class TopN {
    public static class TopNMapper extends Mapper<LongWritable,Text,MyIntWritable,Text>{
        public void map(LongWritable key,Text value,Context context) throws IOException, InterruptedException {
            String line=value.toString();
            if(line.trim().length()>0){
                String str[]=line.split( "," );
                if(str.length==4){
                    context.write( new MyIntWritable( Integer.parseInt( str[2] ) ),new Text( "" ) );
                }
            }
        }
    }

    public static class TopNReducer extends Reducer<MyIntWritable,Text,Text,MyIntWritable>{
        private int index=0;
        public void reduce(MyIntWritable key,Iterable<Text> values,Context context) throws IOException, InterruptedException {
              index++;
              if(index<=5){
                  context.write( new Text( index+" " ),key );
              }
        }
    }

    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {


        org.apache.hadoop.conf.Configuration conf=new org.apache.hadoop.conf.Configuration();
        Job job=new Job(conf,"topn");
        job.setJarByClass( TopN.class );

        job.setMapperClass( TopNMapper.class );
        job.setMapOutputKeyClass( MyIntWritable.class );
        job.setMapOutputValueClass( Text.class );

        job.setReducerClass( TopNReducer.class );
        job.setOutputKeyClass( Text.class);
        job.setOutputValueClass( MyIntWritable.class );

        FileInputFormat.addInputPath( job,new Path( args[0] ) );
        Path outputdir=new Path( args[1] );
        FileSystem fs=FileSystem.get( conf ); //判断输出目录是否存在
        if(fs.exists( outputdir )){
            fs.delete( outputdir,true );
        }
        FileOutputFormat.setOutputPath( job,outputdir ) ;
        System.out.println(job.waitForCompletion( true )?1:0);
    }
}

Scala实现Mapreduce程序2-----Top5