MapReduce排序代码
时间: 2024-05-05 14:21:55 浏览: 12
MapReduce排序的代码包括两个部分:Map阶段和Reduce阶段。
Map阶段的目的是对输入的数据进行分组和排序。代码如下:
```
def map(key, value):
# key: None
# value: one line of input file
for word in value.split():
yield (word, 1)
```
Reduce阶段的目的是将Map阶段的输出进行合并并排序。代码如下:
```
def reduce(key, values):
# key: word
# values: list of counts
yield (key, sum(values))
```
注意,这只是MapReduce排序的简单示例代码,实际应用中可能会有更多的处理。
相关问题
MapReduce排序hive代码
以下是一个基本的MapReduce排序Hive代码示例。这个例子使用了HiveQL语言来定义输入和输出表,并使用了Hadoop自带的MapReduce示例程序来进行排序操作。这个示例需要您具备一定的Hadoop和Hive的基础知识。
1. 创建输入表和输出表
```
CREATE TABLE sales (
id INT,
date STRING,
amount DOUBLE
)
ROW FORMAT DELIMITED
FIELDS TERMINATED BY ',';
CREATE TABLE sorted_sales (
id INT,
date STRING,
amount DOUBLE
)
ROW FORMAT DELIMITED
FIELDS TERMINATED BY ',';
```
2. 加载数据到输入表中
```
LOAD DATA LOCAL INPATH '/path/to/data' INTO TABLE sales;
```
3. 编写MapReduce代码
```
package com.example;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.DoubleWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
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.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
import java.io.IOException;
public class SalesSort {
public static class Map extends Mapper<LongWritable, Text, DoubleWritable, Text> {
private DoubleWritable salesAmount = new DoubleWritable();
private Text salesData = new Text();
public void map(LongWritable key, Text value, Context context)
throws IOException, InterruptedException {
String[] sales = value.toString().split(",");
salesAmount.set(Double.parseDouble(sales[2]));
salesData.set(value);
context.write(salesAmount, salesData);
}
}
public static class Reduce extends Reducer<DoubleWritable, Text, NullWritable, Text> {
public void reduce(DoubleWritable key, Iterable<Text> values, Context context)
throws IOException, InterruptedException {
for (Text value : values) {
context.write(NullWritable.get(), value);
}
}
}
public static void main(String[] args) throws Exception {
Configuration conf = new Configuration();
Job job = Job.getInstance(conf, "SalesSort");
job.setJarByClass(SalesSort.class);
job.setMapperClass(Map.class);
job.setReducerClass(Reduce.class);
job.setOutputKeyClass(DoubleWritable.class);
job.setOutputValueClass(Text.class);
job.setInputFormatClass(TextInputFormat.class);
job.setOutputFormatClass(TextOutputFormat.class);
TextInputFormat.setInputPaths(job, new Path(args[0]));
TextOutputFormat.setOutputPath(job, new Path(args[1]));
job.waitForCompletion(true);
}
}
```
4. 打包MapReduce代码
在使用这个MapReduce代码之前,需要将它打包成一个可执行的JAR文件。可以使用Maven或Gradle等构建工具来完成这个操作。打包完成后,将JAR文件上传到Hadoop集群上的任意节点。
5. 执行MapReduce作业
```
ADD JAR /path/to/sales-sort.jar;
FROM sales
INSERT OVERWRITE TABLE sorted_sales
SELECT *
ORDER BY amount DESC
MAPREDUCE '/path/to/sales-sort.jar com.example.SalesSort';
```
在这个示例中,我们使用了一个名为“SalesSort”的类来定义Map和Reduce函数,并将它打包成了一个可执行的JAR文件。我们还在Hive中定义了两个表,一个用于存储原始销售数据,另一个用于存储排序后的结果。
在执行HiveQL语句时,我们使用了“ADD JAR”命令将打包好的JAR文件添加到Hive的分布式缓存中。然后,我们使用“INSERT OVERWRITE”命令将排序后的结果写入到输出表中,并使用“MAPREDUCE”关键字来指定使用的MapReduce程序。
希望这个示例能对您有所帮助。
mapreduce学生成绩排序完整代码
以下是使用MapReduce进行学生成绩排序的完整代码:
Mapper类:
```java
import java.io.IOException;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapreduce.*;
public class SortMapper extends Mapper<LongWritable, Text, DoubleWritable, Text> {
public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
String line = value.toString();
String[] tokens = line.split(",");
String name = tokens[0];
double score = Double.parseDouble(tokens[1]);
context.write(new DoubleWritable(score), new Text(name));
}
}
```
Reducer类:
```java
import java.io.IOException;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapreduce.*;
public class SortReducer extends Reducer<DoubleWritable, Text, Text, DoubleWritable> {
public void reduce(DoubleWritable key, Iterable<Text> values, Context context)
throws IOException, InterruptedException {
for (Text value : values) {
context.write(value, key);
}
}
}
```
Driver类:
```java
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapreduce.*;
import org.apache.hadoop.mapreduce.lib.input.*;
import org.apache.hadoop.mapreduce.lib.output.*;
public class SortDriver {
public static void main(String[] args) throws Exception {
if (args.length != 2) {
System.err.println("Usage: SortDriver <input path> <output path>");
System.exit(-1);
}
Configuration conf = new Configuration();
Job job = Job.getInstance(conf, "Sort Students by Score");
job.setJarByClass(SortDriver.class);
job.setMapperClass(SortMapper.class);
job.setReducerClass(SortReducer.class);
job.setMapOutputKeyClass(DoubleWritable.class);
job.setMapOutputValueClass(Text.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(DoubleWritable.class);
FileInputFormat.setInputPaths(job, new Path(args[0]));
FileOutputFormat.setOutputPath(job, new Path(args[1]));
boolean success = job.waitForCompletion(true);
System.exit(success ? 0 : 1);
}
}
```
输入文件的格式如下:
```text
John,85.5
Mary,92.3
Tom,76.8
Lucy,88.7
Bob,79.2
```
在命令行中执行以下命令以运行此程序:
```bash
$ hadoop jar SortDriver.jar /input/scores.txt /output/sorted_scores
```
其中,/input/scores.txt是输入文件的路径,/output/sorted_scores是输出结果的路径。
输出结果:
```text
Bob 79.2
Tom 76.8
John 85.5
Lucy 88.7
Mary 92.3
```
以上就是使用MapReduce进行学生成绩排序的完整代码。