I don't really like iterating on components for a third time, but from using GroupingCollection2, I ran into a few issues, plus it seemed to be pretty slow. I'm not sure how heavily used this component is or if people are interested, but I've attempted to write a new one. I checked it into my whiteboard space: http://svn.apache.org/viewvc/incubator/flex/whiteboard/frishy/FastGroupingCollection/ along with some performance tests. For the most part, it's the same as GroupingCollection2, but it doesn't support asynch refresh() and does support nested properties for grouping fields and summary fields.
When using as a basic grouping collection, for larger datasets, it tends to be about 1.5-2x faster than GroupingCollection2. Once you add summary rows, it tends to be much, much faster (50x). If enough people are interested, we can talk about checking it in to the main framework. I've also got a few collection fixes that I'm planning to make once the project gets started a bit more and we have some tests than we can run against. Cheers, Ryan
