hadoop统计以a和b字母开头的单词的个数
时间: 2023-11-12 15:09:09 浏览: 78
您可以使用Hadoop MapReduce来解决这个问题。
首先,您需要编写一个Mapper类来将输入数据拆分为单词并将以a或b开头的单词输出为键值对。例如,如果输入数据是“apple bear cat dog”,则Mapper将生成以下键值对: ("a", "apple"), ("b", "bear")。
然后,您需要编写一个Reducer类来计算每个键的值的数量。例如,如果Mapper产生了键值对 ("a", "apple") 和 ("a", "ant"),则Reducer将输出键值对 ("a", 2)。
最后,您需要将Mapper和Reducer组合在一起,并将它们提交给Hadoop作业进行执行。以下是一个伪代码示例:
```java
public class WordCountMapper extends Mapper<LongWritable, Text, Text, IntWritable> {
private final static IntWritable one = new IntWritable(1);
private Text word = new Text();
public void map(LongWritable key, Text value, Context context)
throws IOException, InterruptedException {
String[] words = value.toString().split("\\s+");
for (String w : words) {
if (w.startsWith("a") || w.startsWith("b")) {
word.set(w);
context.write(word, one);
}
}
}
}
public class WordCountReducer extends Reducer<Text, IntWritable, Text, IntWritable> {
public void reduce(Text key, Iterable<IntWritable> values, Context context)
throws IOException, InterruptedException {
int sum = 0;
for (IntWritable val : values) {
sum += val.get();
}
context.write(key, new IntWritable(sum));
}
}
public class WordCount {
public static void main(String[] args) throws Exception {
Configuration conf = new Configuration();
Job job = Job.getInstance(conf, "word count");
job.setJarByClass(WordCount.class);
job.setMapperClass(WordCountMapper.class);
job.setCombinerClass(WordCountReducer.class);
job.setReducerClass(WordCountReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
FileInputFormat.addInputPath(job, new Path(args[0]));
FileOutputFormat.setOutputPath(job, new Path(args[1]));
System.exit(job.waitForCompletion(true) ? 0 : 1);
}
}
```
在这个示例中,我们假设输入数据是一个文本文件,文件的路径作为第一个命令行参数传递给作业。输出将写入到第二个命令行参数指定的目录中。您可以使用Hadoop命令行工具来运行作业:
```
hadoop jar wordcount.jar WordCount /input /output
```
这将从输入目录读取数据,并将结果写入到输出目录。请注意,输入和输出目录必须在Hadoop文件系统上存在,并且输出目录不能存在。