Correctly add data from last dataset into the target

xfel/merging/application/modify/aux_cosym.py

@@ -307,7 +307,6 @@ def __init__(self, experiments, reflections, uuid_cache_in, params=None,
         datasets = [
             ma.as_anomalous_array().merge_equivalents().array() for ma in datasets
         ]
-
         # opportunity here to subclass as defined above, instead of the dials-implemented version
         self.params.min_reflections = 0 # avoid any further filtering implemented in https://github.com/dials/dials/pull/2741
         self.cosym_analysis = CosymAnalysis(
@@ -360,10 +359,17 @@ def __init__(self, *args, **kwargs):
         self._min_pairs = 3 # minimum number of mutual miller indices for a match
 
         # truncate the input data to save time
-        self._lattices = self._lattices[:10]
+        # self._lattices is the list of start index of each dataset
+        self._lattices = self._lattices[:11]
+
         i_last = self._lattices[-1]
         self._data = self._data[:i_last]
 
+        # now remove the last index in self._lattices as this was just used
+        # to determine the start index of the next dataset (which does not
+        # exist in the cut set)
+        self._lattices = self._lattices[:-1]
+
   def _lattice_lower_upper_index(self, lattice_id):
        lower_index = int(self._lattices[lattice_id])
        upper_index = None