[MAHOUT-900] RandomSeedGenerator samples / output k texts incorrectly

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 0.5
• Fix Version/s: 0.6
• Component/s: Clustering
• Assignee: Sean R. Owen
• Reporter: Sean R. Owen
• Due: 30/Nov/11
• Created: 28/Nov/11 10:40
• Updated: 09/Feb/12 14:00
• Resolved: 28/Nov/11 18:54

Description

          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.