[MAHOUT-1180] Multinomial<T> throws ConcurrentModificationException when iterating and setting probabilities

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 0.8
• Fix Version/s: 0.8
• Assignee: Unassigned
• Reporter: Dan Filimon
• Created: 29/Mar/13 11:19
• Updated: 03/Feb/14 08:05
• Resolved: 03/May/13 11:08

Description

Here's [1] an example of the problem (from BallKMeans, lines 225-232, [2]).

When iterating through the elements in a Multinomial and updating the probabilities, sometimes newWeight becomes 0 (because of using CosineDistances).
When setting a weight to 0 in Multinomial, the element is removed from the items hash map while using the hash map for iteration.
This causes a ConcurrentModificationException.

[1] https://gist.github.com/dfilimon/5270234
[2] https://github.com/dfilimon/mahout/blob/skm/core/src/main/java/org/apache/mahout/clustering/streaming/cluster/BallKMeans.java#L225