Fix mne-tools#4311 (mne-tools#4337)

* Fix mne-tools#4311

* Test for mne-tools#4311

* Test for neighbours

mne/channels/channels.py

@@ -908,8 +908,9 @@ def rename_channels(info, mapping):
 
 def _recursive_flatten(cell, dtype):
     """Unpack mat files in Python."""
-    while not isinstance(cell[0], dtype):
-        cell = [c for d in cell for c in d]
+    if len(cell) > 0:
+        while not isinstance(cell[0], dtype):
+            cell = [c for d in cell for c in d]
     return cell
 
 
@@ -993,7 +994,7 @@ def _ch_neighbor_connectivity(ch_names, neighbors):
         raise ValueError('`ch_names` and `neighbors` must '
                          'have the same length')
     set_neighbors = set([c for d in neighbors for c in d])
-    rest = set(ch_names) - set_neighbors
+    rest = set_neighbors - set(ch_names)
     if len(rest) > 0:
         raise ValueError('Some of your neighbors are not present in the '
                          'list of channel names')

mne/channels/tests/test_channels.py

@@ -12,7 +12,7 @@
 import numpy as np
 from scipy.io import savemat
 from numpy.testing import assert_array_equal
-from nose.tools import assert_raises, assert_true, assert_equal
+from nose.tools import assert_raises, assert_true, assert_equal, assert_false
 
 from mne.channels import rename_channels, read_ch_connectivity
 from mne.channels.channels import _ch_neighbor_connectivity
@@ -161,6 +161,43 @@ def test_read_ch_connectivity():
     assert_equal(len(ch_names), 102)
     assert_raises(ValueError, read_ch_connectivity, 'bananas!')
 
+    # In EGI 256, E31 sensor has no neighbour
+    a = partial(np.array)
+    nbh = np.array([[(['E31'], []),
+                     (['E1'], [[a(['E2'])],
+                               [a(['E3'])]]),
+                     (['E2'], [[a(['E1'])],
+                               [a(['E3'])]]),
+                     (['E3'], [[a(['E1'])],
+                               [a(['E2'])]])]],
+                   dtype=[('label', 'O'), ('neighblabel', 'O')])
+    mat = dict(neighbours=nbh)
+    mat_fname = op.join(tempdir, 'test_isolated_mat.mat')
+    savemat(mat_fname, mat, oned_as='row')
+    ch_connectivity, ch_names = read_ch_connectivity(mat_fname)
+    x = ch_connectivity.todense()
+    assert_equal(x.shape[0], len(ch_names))
+    assert_equal(x.shape, (4, 4))
+    assert_true(np.all(x.diagonal()))
+    assert_false(np.any(x[0, 1:]))
+    assert_false(np.any(x[1:, 0]))
+
+    # Check for neighbours consistency. If a sensor is marked as a neighbour,
+    # then it should also have its neighbours defined.
+    a = partial(np.array)
+    nbh = np.array([[(['E31'], []),
+                     (['E1'], [[a(['E8'])],
+                               [a(['E3'])]]),
+                     (['E2'], [[a(['E1'])],
+                               [a(['E3'])]]),
+                     (['E3'], [[a(['E1'])],
+                               [a(['E2'])]])]],
+                   dtype=[('label', 'O'), ('neighblabel', 'O')])
+    mat = dict(neighbours=nbh)
+    mat_fname = op.join(tempdir, 'test_error_mat.mat')
+    savemat(mat_fname, mat, oned_as='row')
+    assert_raises(ValueError, read_ch_connectivity, mat_fname)
+
 
 def test_get_set_sensor_positions():
     """Test get/set functions for sensor positions"""