我的项目是显示最高,最低和平均温度。我已经完成了,但我必须使用group by key来显示这些功能。我的应用程序中有4个单选按钮,分别为年,月,日和城市。如果我选择一个,那么它会要求我输入聚合函数(max,min,avg)。对于这些我需要更改我的CompositeGroupKey
课程,但我对此一无所知。所以请帮助我,并提供有关代码所需更改的输入。
司机:
import org.apache.hadoop.io.*;
import org.apache.hadoop.fs.*;
import org.apache.hadoop.mapreduce.*;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
public class MaxTemperature
{
public static void Main (String[] args) throws Exception
{
if (args.length != 2)
{
System.err.println("Please Enter the input and output parameters");
System.exit(-1);
}
Job job = new Job();
job.setJarByClass(MaxTemperature.class);
job.setJobName("Max temperature");
FileInputFormat.addInputPath(job,new Path(args[0]));
FileOutputFormat.setOutputPath(job,new Path (args[1]));
job.setMapperClass(MaxTemperatureMapper.class);
job.setReducerClass(MaxTemperatureReducer.class);
job.setMapOutputKeyClass(CompositeGroupKey.class);
job.setMapOutputValueClass(IntWritable.class);
job.setOutputKeyClass(CompositeGroupKey.class);
job.setOutputValueClass(DoubleWritable.class);
System.exit(job.waitForCompletion(true)?0:1);
}
}
映射器:
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapreduce.*;
import java.io.IOException;
public class MaxTemperatureMapper extends Mapper <LongWritable, Text, CompositeGroupKey, IntWritable>
{
public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException
{
String line = value.toString();
int year = Integer.parseInt(line.substring(0,4));
String mnth = line.substring(7,10);
int date = Integer.parseInt(line.substring(10,12));
int temp= Integer.parseInt(line.substring(12,14));
CompositeGroupKey cntry = new CompositeGroupKey(year,mnth, date);
context.write(cntry, new IntWritable(temp));
}
}
减速器:
import org.apache.hadoop.io.DoubleWritable;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.mapreduce.*;
import java.io.IOException;
public class MaxTemperatureReducer extends Reducer <CompositeGroupKey, IntWritable, CompositeGroupKey, CompositeGroupkeyall >{
public void reduce(CompositeGroupKey key, Iterable<IntWritable> values , Context context) throws IOException,InterruptedException
{
Double max = Double.MIN_VALUE;
Double min =Double.MAX_VALUE;
for (IntWritable value : values )
{
min = Math.min(min, value.get());
max = Math.max(max, value.get());
}
CompositeGroupkeyall val =new CompositeGroupkeyall(max,min);
context.write(key, val);
}
}
复合键:
import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import org.apache.hadoop.io.WritableComparable;
import org.apache.hadoop.io.WritableUtils;
class CompositeGroupKey implements WritableComparable<CompositeGroupKey> {
int year;
String mnth;
int date;
CompositeGroupKey(int y, String c, int d){
year = y;
mnth = c;
date = d;
}
CompositeGroupKey(){}
public void write(DataOutput out) throws IOException {
out.writeInt(year);
WritableUtils.writeString(out, mnth);
out.writeInt(date);
}
public void readFields(DataInput in) throws IOException {
this.year = in.readInt();
this.mnth = WritableUtils.readString(in);
this.date = in.readInt();
}
public int compareTo(CompositeGroupKey pop) {
if (pop == null)
return 0;
int intcnt;
intcnt = Integer.valueOf(year).toString().compareTo(Integer.valueOf(pop.year).toString());
if(intcnt != 0){
return intcnt;
}else if(mnth.compareTo(pop.mnth) != 0){
return mnth.compareTo(pop.mnth);
}else{
return Integer.valueOf(date).toString().compareTo(Integer.valueOf(pop.date).toString());
}
}
public String toString() {
return year + " :" + mnth.toString() + " :" + date;
}
}
import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import org.apache.hadoop.io.WritableComparable;
class CompositeGroupkeyall implements WritableComparable<CompositeGroupkeyall> {
Double max;
Double min;
CompositeGroupkeyall(double x, double y){
max = x ;
min = y ;
}
CompositeGroupkeyall(){}
public void readFields(DataInput in) throws IOException {
this.max = in.readDouble();
this.min = in.readDouble();
}
public void write(DataOutput out) throws IOException {
out.writeDouble(max);
out.writeDouble(min);
}
public int compareTo(CompositeGroupkeyall arg0) {
return -1;
}
public String toString() {
return max + " " + min +" " ;
}
}
答案 0 :(得分:0)
您可以创建更多的键值对,并让相同的reducer处理数据,所有日期/月/年将由同一个reducer处理
CompositeGroupKey cntry = new CompositeGroupKey(year, mnth, date);
CompositeGroupKey cntry_date = new CompositeGroupKey((int)0, "ALL", date);
CompositeGroupKey cntry_mnth = new CompositeGroupKey((int)0, mnth, (int) 1);
CompositeGroupKey cntry_year = new CompositeGroupKey(year, "ALL", (int) 1);
context.write(cntry, new IntWritable(temp));
context.write(cntry_date, new IntWritable(temp));
context.write(cntry_mnth, new IntWritable(temp));
context.write(cntry_year, new IntWritable(temp));