Fix empty list in reports

* this is a temporary solution until
  BlueBrain/libsonata#84 is done

bluepysnap/frame_report.py

@@ -19,6 +19,7 @@
 
 from cached_property import cached_property
 from pathlib2 import Path
+import numpy as np
 import pandas as pd
 from libsonata import ElementReportReader
 
@@ -211,6 +212,10 @@ def nodes(self):
 
     def _resolve(self, group):
         """Transform a group into a node_id array."""
+        if group == []:
+            # Only solution to return an empty list from self._frame_population.get
+            # see: https://github.com/BlueBrain/libsonata/issues/84
+            return np.array([-2])
         return self.nodes.ids(group=group)
 
 

bluepysnap/spike_report.py

@@ -84,6 +84,10 @@ def nodes(self):
 
     def _resolve_nodes(self, group):
         """Transform a node group into a node_id array."""
+        if group == []:
+            # Only solution to return an empty list from self._spike_population.get
+            # see: https://github.com/BlueBrain/libsonata/issues/84
+            return np.array([-2])
         return self.nodes.ids(group=group)
 
     def get(self, group=None, t_start=None, t_stop=None):

tests/test_frame_report.py

@@ -142,6 +142,8 @@ def test_nodes_invalid_population(self):
     def test_get(self):
         pdt.assert_frame_equal(self.test_obj.get(), self.df)
 
+        pdt.assert_frame_equal(self.test_obj.get([]),  pd.DataFrame())
+
         pdt.assert_frame_equal(self.test_obj.get(2), self.df.loc[:, [2]])
 
         pdt.assert_frame_equal(self.test_obj.get([2, 0]), self.df.loc[:, [0, 2]])

tests/test_spike_report.py

@@ -105,7 +105,7 @@ def test__resolve_nodes(self):
     def test_get(self):
         pdt.assert_series_equal(self.test_obj.get(),
                                 _create_series([2, 0, 1, 2, 0], [0.1, 0.2, 0.3, 0.7, 1.3]))
-
+        pdt.assert_series_equal(self.test_obj.get([]), _create_series([], []))
         npt.assert_allclose(self.test_obj.get(2), np.array([0.1, 0.7]))
         npt.assert_allclose(self.test_obj.get(0, t_start=1.), [1.3])
         npt.assert_allclose(self.test_obj.get(0, t_stop=1.), [0.2])