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https://issues.apache.org/jira/browse/MAHOUT-353?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12851789#action_12851789
]
Hui Wen Han commented on MAHOUT-353:
------------------------------------
org.apache.mahout.cf.taste.impl.common.Cache
private V getAndCacheValue(K key) throws TasteException {
V value = retriever.get(key); //we may get null here,if so ,we can not
put the value to cache (FastMap).
synchronized (cache) {
cache.put(key, value);
}
return value;
}
because in UserVectorToCooccurrenceReducer:
line49: while (cooccurrences.hasNext()) {
Vector.Element element = cooccurrences.next();
if (element.get() <= 1.0) { // purge small values
element.set(0.0); //here we set element to zero
}
}
in RecommenderMapper:
line 103: Iterator<Vector.Element> userVectorIterator =
userVector.iterateNonZero(); //here not get Zero item
Vector recommendationVector = new
RandomAccessSparseVector(Integer.MAX_VALUE, 1000);
while (userVectorIterator.hasNext()) {
Vector.Element element = userVectorIterator.next();
int index = element.index();
double value = element.get();
Vector columnVector;
try {
columnVector = cooccurrenceColumnCache.get(new IntWritable(index));
//here may get null
so we need :
in org.apache.mahout.cf.taste.impl.common.Cache
private V getAndCacheValue(K key) throws TasteException {
V value = retriever.get(key); //we may get null here,if so ,we can not
put the value to cache (FastMap).
if (value == null)
{
return null;
}
synchronized (cache) {
cache.put(key, value);
}
return value;
}
in RecommenderMapper:
while (userVectorIterator.hasNext()) {
Vector.Element element = userVectorIterator.next();
int index = element.index();
double value = element.get();
Vector columnVector;
try {
columnVector = cooccurrenceColumnCache.get(new IntWritable(index));
} catch (TasteException te) {
if (te.getCause() instanceof IOException) {
throw (IOException) te.getCause();
} else {
throw new IOException(te.getCause());
}
}
if (columnVector !=null)
{
columnVector.times(value).addTo(recommendationVector);
}
}
> java.lang.NullPointerException in RecommenderMapper
> ---------------------------------------------------
>
> Key: MAHOUT-353
> URL: https://issues.apache.org/jira/browse/MAHOUT-353
> Project: Mahout
> Issue Type: Bug
> Components: Collaborative Filtering
> Affects Versions: 0.4
> Reporter: Hui Wen Han
> Fix For: 0.4
>
>
> java.lang.NullPointerException
> at
> org.apache.mahout.cf.taste.hadoop.item.RecommenderMapper$CooccurrenceCache.get(RecommenderMapper.java:169)
> at
> org.apache.mahout.cf.taste.hadoop.item.RecommenderMapper$CooccurrenceCache.get(RecommenderMapper.java:154)
> at
> org.apache.mahout.cf.taste.impl.common.Cache.getAndCacheValue(Cache.java:125)
> at org.apache.mahout.cf.taste.impl.common.Cache.get(Cache.java:94)
> at
> org.apache.mahout.cf.taste.hadoop.item.RecommenderMapper.map(RecommenderMapper.java:111)
> at
> org.apache.mahout.cf.taste.hadoop.item.RecommenderMapper.map(RecommenderMapper.java:52)
> at org.apache.hadoop.mapred.MapRunner.run(MapRunner.java:50)
> at org.apache.hadoop.mapred.MapTask.runOldMapper(MapTask.java:358)
> at org.apache.hadoop.mapred.MapTask.run(MapTask.java:307)
> at org.apache.hadoop.mapred.Child.main(Child.java:170)
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