java - 使用java计算入度和出度并显示总和的Mapreduce函数

Question

我正在尝试对一组数据的入度和出度进行求和。这是示例数据:

Source  Target

1        2  
2        1  
3        1  
2        3  

所以预期的输出是:

ID     In degree   Out degree  
1       2            1  
2       1            2  
3       1            1  

如何使用 Java 的 MapReduce 来实现这一点并在一行中打印出结果。

Answer 1

涉及一项 MR 工作的一个选项:假设原始数据集看起来像[node1,node2]:

-mapper 读取原始数据集并为每一行发出三元组 [node1,out] 和 [node2,in]

-reducer 以 [key,label] 形式从映射器获取三元组，通过分别计算每个键的“out”标签和“in”标签来计算出度和入度，并以以下形式输出[键、入度、出度]

实现将类似于以下内容(假设数据集中的 node1 和 node2 由空格分隔，并且还假设数据集仅包含不同的对):

映射器:

public class YourMapper extends MapReduceBase implements Mapper<LongWritable, Text, Text, Text> {

      public void map(LongWritable key, Text value, OutputCollector<Text, Text> output, Reporter reporter) throws IOException {

        String line = value.toString();     
        String[] line_spl = line.split(" ");

        String node1 = line_spl[0];
        String node2 = line_spl[1];

        Text node1_txt = new Text(node1);
        Text node2_txt = new Text(node2);
        Text emit_out = new Text("out");
        Text emit_in  = new Text("in");

        output.collect(node1_txt, emit_out);
        output.collect(node2_txt, emit_in );

      }//end map function


}//end mapper class

reducer :

public class YourReducer extends MapReduceBase implements Reducer<Text, Text, Text, Text> {

    public void reduce(Text key, Iterator<Text> values, OutputCollector<Text, Text> output, Reporter reporter) throws IOException {

         int count_outs = 0;
         int count_ins  = 0;

            while (values.hasNext()) {

              Text value = (Text) values.next();

              String value_str = value.toString();

              if(value_str.equals("out"))
                 count_outs++;
              else
              if(value_str.equals("in"))
                 count_ins++;  

            }

            Text out = new Text(count_ins + " " + count_outs);              
            output.collect(key, out);

    }//end reduce function

}//end reducer class