Refactor offline

This refactoring includes some slicing and performance improvement attempts.

The slicing is still experimental and has some flaws:

• fancy indexing over thousands of elements might be horrible slow, eg f.events.tracks[idx_list, 0] where idx_list is a huge list of indices
• trivial problem of iterating: for track in f.evens.tracks does not stop after the last element
• meaningless indexing: f.events[5][23][420] is simply f.events[420] since the index/slice is not chained but overwritten when propagated. We need custom checks whether it makes sense
  • events are flat lists, so [x][y] does not make sense, it should throw an error
  • f.events[5:23][4] should effectively be the same as f.events[9] due to chaining of slice/index

km3io/offline.py

@@ -7,6 +7,10 @@ from .tools import Branch, BranchMapper, cached_property, _to_num
 MAIN_TREE_NAME = "E"
 EXCLUDE_KEYS = ["AAObject", "t", "fBits", "fUniqueID"]
 
+# 110 MB based on the size of the largest basket found so far in km3net
+BASKET_CACHE_SIZE = 110 * 1024**2
+BASKET_CACHE = uproot.cache.ThreadSafeArrayCache(BASKET_CACHE_SIZE)
+
 
 def _nested_mapper(key):
     """Maps a key in the ROOT file to another key (e.g. trks.pos.x -> pos_x)"""