ShapeOut 2.15.0

For this release, I focused mostly on code optimization. There is a significant speed-up with dclab 0.57.0 for plotting (10x faster downsampling, 100x faster mapping of hierarchy children data) and data export (4x faster filtering operations, dataset chunking by 1MiB instead of 100 events or none at all). In Shape-Out, there are minor speed-ups with statistics caching.

• enh: avoid creating hierarchy when no filters are applied (speed)
• enh: cache computed statistics
• ref: avoid division-by-zero warning
• setup: bump dclab from 0.56.3 to 0.57.0 (speed)