mapreduce项目统计hbase成绩表中 单科最高单科排名、总分排名代码

### 回答1：
下面是一个使用 MapReduce 统计 HBase 成绩表中单科最高单科排名和总分排名的示例代码：

import java.io.IOException;
import java.util.StringTokenizer;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.client.Result;
import org.apache.hadoop.hbase.client.Scan;
import org.apache.hadoop.hbase.io.ImmutableBytesWritable;
import org.apache.hadoop.hbase.mapreduce.TableMapReduceUtil;
import org.apache.hadoop.hbase.mapreduce.TableMapper;
import org.apache.hadoop.hbase.util.Bytes;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.output.NullOutputFormat;

public class RankingCalculator {

  public static class RankingMapper extends TableMapper<Text, IntWritable> {
    private static final byte[] CF = "scores".getBytes();
    private static final byte[] ATTR1 = "math".getBytes();
    private static final byte[] ATTR2 = "english".getBytes();
    private static final byte[] ATTR3 = "history".getBytes();

    private final IntWritable score = new IntWritable();
    private final Text subject = new Text();

    @Override
    public void map(ImmutableBytesWritable row, Result value, Context context)
        throws IOException, InterruptedException {
      // 读取每个学生的数学、英语和历史成绩
      int mathScore = Bytes.toInt(value.getValue(CF, ATTR1));
      int englishScore = Bytes.toInt(value.getValue(CF, ATTR2));
      int historyScore = Bytes.toInt(value.getValue(CF, ATTR3));

      // 输出每科的最高分
      subject.set("math");
      score.set(mathScore);
      context.write(subject, score);
      subject.set("english");
      score.set(englishScore);
      context.write(subject, score);
      subject.set("history");
      score.set(historyScore);
      context.write(subject, score);

      // 输出总分
      subject.set("total");
      score.set(mathScore + englishScore + historyScore);
      context.write(subject, score);
    }
  }

  public static class RankingReducer extends Reducer<Text, IntWritable,  

### 回答2：
在MapReduce项目中，我们可以使用HBase成绩表进行单科最高单科排名和总分排名的统计。以下是代码的示例：

首先，我们需要编写一个Map类，将HBase表中的每一行数据拆分为键值对，其中键是学生ID，值是学生成绩信息。

public static class MyMapper extends TableMapper<Text, IntWritable> {
private static final byte[] COLUMN_FAMILY = "cf".getBytes();
private static final byte[] QUALIFIER = "score".getBytes();

private Text outKey = new Text();
private IntWritable outValue = new IntWritable();

@Override
protected void map(ImmutableBytesWritable rowKey, Result result, Context context) throws IOException, InterruptedException {
String studentId = new String(rowKey.get());
int score = Bytes.toInt(result.getValue(COLUMN_FAMILY, QUALIFIER));

// 输出每个学生的单科成绩
outKey.set(studentId);
outValue.set(score);
context.write(outKey, outValue);
}
}

接下来，我们需要编写一个Reduce类，将相同学生ID的成绩聚合在一起，并计算单科最高单科排名和总分排名。

public static class MyReducer extends Reducer<Text, IntWritable, Text, Text> {
private Text outValue = new Text();

@Override
protected void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
int maxScore = 0;
int totalScore = 0;
int count = 0;

for (IntWritable value : values) {
int score = value.get();

// 计算单科最高单科排名
if (score > maxScore) {
maxScore = score;
}

totalScore += score;
count++;
}

// 输出学生的单科最高单科排名和总分排名
String result = "单科最高单科排名：" + maxScore + ", 总分排名：" + totalScore / count;
outValue.set(result);
context.write(key, outValue);
}
}

最后，我们需要编写一个Driver类，设置MapReduce作业的输入输出路径、使用的Mapper和Reduce类等相关信息。

public int run(String[] args) throws Exception {
Configuration conf = getConf();
Job job = Job.getInstance(conf, "Statistics");

job.setJarByClass(Statistics.class);
TableMapReduceUtil.initTableMapperJob("hbase_table", new Scan(), MyMapper.class, Text.class, IntWritable.class, job);
job.setReducerClass(MyReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(Text.class);

FileOutputFormat.setOutputPath(job, new Path(args[0]));

return job.waitForCompletion(true) ? 0 : 1;
}

public static void main(String[] args) throws Exception {
int exitCode = ToolRunner.run(new Statistics(), args);
System.exit(exitCode);
}

以上是使用MapReduce项目统计HBase成绩表中单科最高单科排名和总分排名的代码示例，你可以根据实际需求进行适当调整。