FIX: Fix epoch eq with no events

mne/epochs.py

@@ -2326,6 +2326,9 @@ def _minimize_time_diff(t_shorter, t_longer):
     """Find a boolean mask to minimize timing differences"""
     from scipy.interpolate import interp1d
     keep = np.ones((len(t_longer)), dtype=bool)
+    if len(t_shorter) == 0:
+        keep.fill(False)
+        return keep
     scores = np.ones((len(t_longer)))
     x1 = np.arange(len(t_shorter))
     # The first set of keep masks to test

mne/tests/test_epochs.py

@@ -1361,6 +1361,13 @@ def test_epoch_eq():
         assert_raises(ValueError, epochs.equalize_event_counts, c, copy=False)
     assert_raises(KeyError, epochs.equalize_event_counts,
                   ["a/no_match", "b"], copy=False)
+    # test equalization with no events of one type
+    epochs.drop(np.arange(10))
+    assert_equal(len(epochs['a/x']), 0)
+    assert_true(len(epochs['a/y']) > 0)
+    epochs.equalize_event_counts(['a/x', 'a/y'], copy=False)
+    assert_equal(len(epochs['a/x']), 0)
+    assert_equal(len(epochs['a/y']), 0)
 
 
 def test_access_by_name():