This topic describes an example of using Unique in MapReduce.

Preparations

  1. Prepare the JAR package of the test program. In this topic, the JAR package is named mapreduce-examples.jar and stored in the local path data\resources.
  2. Prepare test tables and resources for Unique.
    1. Create test tables.
      create table ss_in(key bigint, value bigint);
      create table ss_out(key bigint, value bigint);
    2. Add test resources.
      add jar data\resources\mapreduce-examples.jar -f;
  3. Use Tunnel to import data.
    tunnel upload data ss_in;
    The following data is imported to the ss_in table:
     1,1
     1,1
     2,2
     2,2

Procedure

Run Unique on the MaxCompute client.
jar -resources mapreduce-examples.jar -classpath data\resources\mapreduce-examples.jar
com.aliyun.odps.mapred.open.example.Unique ss_in ss_out key;

Expected result

The job runs normally. The following data is returned in the ss_out table:
+------------+------------+
| key        | value      |
+------------+------------+
| 1          |   1        |
| 2          |   2        |
+------------+------------+

Sample code

package com.aliyun.odps.mapred.open.example;
import java.io.IOException;
import java.util.Iterator;
import com.aliyun.odps.data.Record;
import com.aliyun.odps.data.TableInfo;
import com.aliyun.odps.mapred.JobClient;
import com.aliyun.odps.mapred.MapperBase;
import com.aliyun.odps.mapred.ReducerBase;
import com.aliyun.odps.mapred.TaskContext;
import com.aliyun.odps.mapred.conf.JobConf;
import com.aliyun.odps.mapred.utils.InputUtils;
import com.aliyun.odps.mapred.utils.OutputUtils;
import com.aliyun.odps.mapred.utils.SchemaUtils;
/**
     * Unique Remove duplicate words
     *
     **/
public class Unique {
    public static class OutputSchemaMapper extends MapperBase {
        private Record key;
        private Record value;
        @Override
            public void setup(TaskContext context) throws IOException {
            key = context.createMapOutputKeyRecord();
            value = context.createMapOutputValueRecord();
        }
        @Override
            public void map(long recordNum, Record record, TaskContext context)
            throws IOException {
            long left = 0;
            long right = 0;
            if (record.getColumnCount() > 0) {
                left = (Long) record.get(0);
                if (record.getColumnCount() > 1) {
                    right = (Long) record.get(1);
                }
                key.set(new Object[] { (Long) left, (Long) right });
                value.set(new Object[] { (Long) left, (Long) right });
                context.write(key, value);
            }
        }
    }
    public static class OutputSchemaReducer extends ReducerBase {
        private Record result = null;
        @Override
            public void setup(TaskContext context) throws IOException {
            result = context.createOutputRecord();
        }
        @Override
            public void reduce(Record key, Iterator<Record> values, TaskContext context)
            throws IOException {
            result.set(0, key.get(0));
            while (values.hasNext()) {
                Record value = values.next();
                result.set(1, value.get(1));
            }
            context.write(result);
        }
    }
    public static void main(String[] args) throws Exception {
        if (args.length > 3 || args.length < 2) {
            System.err.println("Usage: unique <in> <out> [key|value|all]");
            System.exit(2);
        }
        String ops = "all";
        if (args.length == 3) {
            ops = args[2];
        }
        /** The input group of Reduce is determined by the value of the setOutputGroupingColumns parameter. If this parameter is not specified, the default value MapOutputKeySchema is used. */
        // Key Unique
        if (ops.equals("key")) {
            JobConf job = new JobConf();
            job.setMapperClass(OutputSchemaMapper.class);
            job.setReducerClass(OutputSchemaReducer.class);
            job.setMapOutputKeySchema(SchemaUtils.fromString("key:bigint,value:bigint"));
            job.setMapOutputValueSchema(SchemaUtils.fromString("key:bigint,value:bigint"));
            job.setPartitionColumns(new String[] { "key" });
            job.setOutputKeySortColumns(new String[] { "key", "value" });
            job.setOutputGroupingColumns(new String[] { "key" });
            job.set("tablename2", args[1]);
            job.setNumReduceTasks(1);
            job.setInt("table.counter", 0);
            InputUtils.addTable(TableInfo.builder().tableName(args[0]).build(), job);
            OutputUtils.addTable(TableInfo.builder().tableName(args[1]).build(), job);
            JobClient.runJob(job);
        }
        // Key&Value Unique
        if (ops.equals("all")) {
            JobConf job = new JobConf();
            job.setMapperClass(OutputSchemaMapper.class);
            job.setReducerClass(OutputSchemaReducer.class);
            job.setMapOutputKeySchema(SchemaUtils.fromString("key:bigint,value:bigint"));
            job.setMapOutputValueSchema(SchemaUtils.fromString("key:bigint,value:bigint"));
            job.setPartitionColumns(new String[] { "key" });
            job.setOutputKeySortColumns(new String[] { "key", "value" });
            job.setOutputGroupingColumns(new String[] { "key", "value" });
            job.set("tablename2", args[1]);
            job.setNumReduceTasks(1);
            job.setInt("table.counter", 0);
            InputUtils.addTable(TableInfo.builder().tableName(args[0]).build(), job);
            OutputUtils.addTable(TableInfo.builder().tableName(args[1]).build(), job);
            JobClient.runJob(job);
        }
        // Value Unique
        if (ops.equals("value")) {
            JobConf job = new JobConf();
            job.setMapperClass(OutputSchemaMapper.class);
            job.setReducerClass(OutputSchemaReducer.class);
            job.setMapOutputKeySchema(SchemaUtils.fromString("key:bigint,value:bigint"));
            job.setMapOutputValueSchema(SchemaUtils.fromString("key:bigint,value:bigint"));
            job.setPartitionColumns(new String[] { "value" });
            job.setOutputKeySortColumns(new String[] { "value" });
            job.setOutputGroupingColumns(new String[] { "value" });
            job.set("tablename2", args[1]);
            job.setNumReduceTasks(1);
            job.setInt("table.counter", 0);
            InputUtils.addTable(TableInfo.builder().tableName(args[0]).build(), job);
            OutputUtils.addTable(TableInfo.builder().tableName(args[1]).build(), job);
            JobClient.runJob(job);
        }
    }
}