Strange results - I obtain same value for all keys
- by Pietro Luciani
I have a problem with mapreduce. Giving as input a list of song ("Songname"#"UserID"#"boolean") i must have as result a song list in which is specified how many time different useres listen them... so a output ("Songname","timelistening").
I used hashtable to allow only one couple .
With short files it works well but when I put as input a list about 1000000 of records it returns me the same value (20) for all records.
This is my mapper:
public static class CanzoniMapper extends Mapper<Object, Text, Text, IntWritable>{
private IntWritable userID = new IntWritable(0);
private Text song = new Text();
public void map(Object key, Text value, Context context) throws IOException, InterruptedException {
/*StringTokenizer itr = new StringTokenizer(value.toString());
while (itr.hasMoreTokens()) {
word.set(itr.nextToken());
context.write(word, one);
}*/
String[] caratteri = value.toString().split("#");
if(caratteri[2].equals("1")){
song.set(caratteri[0]);
userID.set(Integer.parseInt(caratteri[1]));
context.write(song,userID);
}
}
}
This is my reducer:
public static class CanzoniReducer extends Reducer<Text,IntWritable,Text,IntWritable> {
private IntWritable result = new IntWritable();
public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
Hashtable<IntWritable,Text> doppioni = new Hashtable<IntWritable,Text>();
for (IntWritable val : values) {
doppioni.put(val,key);
}
result.set(doppioni.size());
//doppioni.clear();
context.write(key,result);
}
}
and main:
Configuration conf = new Configuration();
Job job = new Job(conf, "word count");
job.setJarByClass(Canzoni.class);
job.setMapperClass(CanzoniMapper.class);
//job.setCombinerClass(CanzoniReducer.class);
//job.setNumReduceTasks(2);
job.setReducerClass(CanzoniReducer.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);
Any idea???
