RandomSeedGenerator samples / output k texts incorrectly
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Key: MAHOUT-900
URL: https://issues.apache.org/jira/browse/MAHOUT-900
Project: Mahout
Issue Type: Bug
Components: Clustering
Affects Versions: 0.5
Reporter: Sean Owen
Assignee: Robin Anil
Priority: Minor
Fix For: 0.6
Attachments: MAHOUT-900.patch
int currentSize = chosenTexts.size();
if (currentSize < k) {
chosenTexts.add(newText);
chosenClusters.add(newCluster);
} else if (random.nextInt(currentSize + 1) == 0) { // with chance
1/(currentSize+1) pick new element
int indexToRemove = random.nextInt(currentSize); // evict one
chosen randomly
chosenTexts.remove(indexToRemove);
chosenClusters.remove(indexToRemove);
chosenTexts.add(newText);
chosenClusters.add(newCluster);
}
The second "if" condition ought to be "!= 0", right? Only if it is 0 do we skip
the body, which removes an existing element, since the new element itself is
evicted.
Second, this code:
for (int i = 0; i < k; i++) {
writer.append(chosenTexts.get(i), chosenClusters.get(i));
}
... assumes that at least k elements existed in the input, and fails otherwise.
Probably need to cap this.
Patch attached.
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