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https://issues.apache.org/jira/browse/MAHOUT-1083?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jeff Eastman updated MAHOUT-1083:
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Attachment: MAHOUT-1083.patch
Oh Yikes! This is another example of the Hadoop platform reusing a single
instance of the Writable every time another one is read from the input stream.
Every time iter.next() is called, the same object (cw == first) will be
returned. This does not show up in unit tests because only a single reducer is
ever used. It explains exactly the odd clustering behavior you have observed.
Here's a patch that *may* fix the problem. I believe that ClusterWritable will
create a new instance for its value instVar even if the same ClusterWritable is
used.
Please try this and see if it resolves the issue.
> CIReducer in kmeans doesn't work well
> -------------------------------------
>
> Key: MAHOUT-1083
> URL: https://issues.apache.org/jira/browse/MAHOUT-1083
> Project: Mahout
> Issue Type: Bug
> Environment: hadoop-2.0.0-alpha: pseudo cluster and single node
> cluster hadoop-1.0.3: pseudo cluster hadoop-0.20.2:pseudo cluster
> mahout: mahout-0.7 os: ubuntu 11.04 jdk: jdk1.6.0_27
> Reporter: liutengfei
> Attachments: MAHOUT-1083.patch
>
>
> the function "reduce" in mahout-0.7-kmeans-CIReducer.java doesn't work well
> as it looks like.
> protected void reduce(IntWritable key, Iterable<ClusterWritable> values,
> Context context) throws IOException,
> InterruptedException {
> Iterator<ClusterWritable> iter = values.iterator();
> ClusterWritable first = null;
> while (iter.hasNext()) {
> ClusterWritable cw = iter.next();
> if (first == null) {
> first = cw;
> } else {
> first.getValue().observe(cw.getValue());
> }
> }
> List<Cluster> models = new ArrayList<Cluster>();
> models.add(first.getValue());
> classifier = new ClusterClassifier(models, policy);
> classifier.close();
> context.write(key, first);
> }
> Apparently， the variable "first" will collect all output data of maps.
> Actually but, the value of "first" will change after the code
> "ClusterWritable cw = iter.next();", same with this new variable "cw"! I
> don't why but running result shows that the code runs looks like
> this:"ClusterWritable cw = first = iter.next();".
> is "cw" a reference a to "iter"?
> is "iter.next" just change the value of "iter" itself to the next?
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