Add preliminary attempts for slicing magic

km3io/offline.py

 import uproot
 import numpy as np
+
 import warnings
 import km3io.definitions.trigger
 import km3io.definitions.fitparameters
@@ -794,6 +795,11 @@ class OfflineTracks:
         if isinstance(item, int):
             return OfflineTrack(self._keys, [v[item] for v in self._values],
                                 fitparameters=self._fitparameters)
+        elif isinstance(item, list) and all(isinstance(i, str) for i in item):
+            cols = item
+            data = [getattr(self, c) for c in cols]
+            dtype = dict(names=cols, formats=[d.dtype for d in data])
+            return np.rec.fromarrays(data, dtype=dtype)
         else:
             return OfflineTracks(self._keys, [v[item] for v in self._values],
                                  fitparameters=self._fitparameters)

tests/test_offline.py

@@ -419,6 +419,11 @@ class TestOfflineTracks(unittest.TestCase):
             self.assertListEqual(list(tracks.E[:, 0][_slice]),
                                  list(tracks[_slice].E[:, 0]))
 
+    def test_slicing_via_columns(self):
+        tracks = self.tracks
+        data = tracks[['E', 'lik']]
+        assert 1 == data.E
+
 
 class TestOfflineTrack(unittest.TestCase):
     def setUp(self):