hadoop mapreduce数据排序
hadoop mapreduce数据排序
有如下3个输入文件:
file0
[plain]
2
32
654
32
15
756
65223
file1
[plain]
5956
22
650
92
file2
[plain]
26
54
6
由于reduce获得的key是按字典顺序排序的,利用默认的规则即可。
[java]
// map将输入中的value化成IntWritable类型,作为输出的key
public static class Map extends
Mapper<Object, Text, IntWritable, IntWritable> {
private static IntWritable data = new IntWritable();
// 实现map函数
public void map(Object key, Text value, Context context)
throws IOException, InterruptedException {
String line = value.toString();
data.set(Integer.parseInt(line));
context.write(data, new IntWritable(1));
}
}
// reduce将输入中的key复制到输出数据的key上,
// 然后根据输入的value-list中元素的个数决定key的输出次数
// 用全局linenum来代表key的位次
public static class Reduce extends
Reducer<IntWritable, IntWritable, IntWritable, IntWritable> {
private static IntWritable linenum = new IntWritable(1);
// 实现reduce函数
public void reduce(IntWritable key, Iterable<IntWritable> values,
Context context) throws IOException, InterruptedException {
for (IntWritable val : values) {
context.write(linenum, key);
linenum = new IntWritable(linenum.get() + 1);
}
}
}
输出如下:
[plain]
1 2
2 6
3 15
4 22
5 26
6 32
7 32
8 54
9 92
10 650
11 654
12 756
13 5956
14 65223