Preserve sample timestamps when slicing AnalogSignal

doc/source/authors.rst

@@ -106,6 +106,7 @@ and may not be the current affiliation of a contributor.
 * Aditya Singh (github)
 * Stanley C.
 * Axel Coiffard-Donaty
+* Anton Soloviev
 
 1. Centre de Recherche en Neuroscience de Lyon, CNRS UMR5292 - INSERM U1028 - Université Claude Bernard Lyon 1
 2. Unité de Neuroscience, Information et Complexité, CNRS UPR 3293, Gif-sur-Yvette, France

neo/core/analogsignal.py

@@ -311,10 +311,9 @@ def __getitem__(self, i):
                 obj = pq.Quantity(obj.magnitude, units=obj.units)
             else:
                 if isinstance(j, slice):
-                    if j.start:
-                        obj.t_start = self.t_start + j.start * self.sampling_period
-                    if j.step:
-                        obj.sampling_period *= j.step
+                    start, _, step = j.indices(len(self))
+                    obj.t_start = self.t_start + start * self.sampling_period
+                    obj.sampling_period = self.sampling_period * step
                 elif isinstance(j, np.ndarray):
                     raise NotImplementedError("Arrays not yet supported")  # in the general case, would need to return
                     #  IrregularlySampledSignal(Array)
@@ -329,8 +328,9 @@ def __getitem__(self, i):
                 obj.array_annotate(**deepcopy(self.array_annotations_at_index(k)))
         elif isinstance(i, slice):
             obj = super().__getitem__(i)
-            if i.start:
-                obj.t_start = self.t_start + i.start * self.sampling_period
+            start, _, step = i.indices(len(self))
+            obj.t_start = self.t_start + start * self.sampling_period
+            obj.sampling_period = self.sampling_period * step
             obj.array_annotations = deepcopy(self.array_annotations)
         elif isinstance(i, np.ndarray):
             # Indexing of an AnalogSignal is only consistent if the resulting number of

neo/test/coretest/test_analogsignal.py

@@ -600,6 +600,41 @@ def test__slice_should_change_sampling_period(self):
         assert_array_equal(result2.magnitude, self.data1[::2, :1])
         assert_array_equal(result3.magnitude, self.data1[1:7:2, :1])
 
+    def test__slice_timestamps_match_selected_samples(self):
+        signal = AnalogSignal(np.arange(40).reshape(20, 2), units="uV", sampling_rate=4 * pq.Hz, t_start=2 * pq.s)
+        original_times = signal.times.copy()
+        original_period = signal.sampling_period.copy()
+        slices = (
+            slice(None, None, 2),
+            slice(3, 17, 3),
+            slice(-5, None),
+            slice(-12, -2, 2),
+            slice(-100, None, 3),
+            slice(None, None, -1),
+            slice(17, 2, -3),
+            slice(100, None, -2),
+        )
+        for time_slice in slices:
+            for channel_slice in (None, slice(None), 1):
+                with self.subTest(time_slice=time_slice, channel_slice=channel_slice):
+                    if channel_slice is None:
+                        result = signal[time_slice]
+                        expected_data = signal.magnitude[time_slice]
+                    else:
+                        result = signal[time_slice, channel_slice]
+                        expected_data = signal.magnitude[time_slice, channel_slice].reshape(result.shape)
+                    assert_array_equal(result.magnitude, expected_data)
+                    assert_array_equal(result.times, original_times[time_slice])
+                    self.assertEqual(result.sampling_period, original_period * (time_slice.step or 1))
+        assert_array_equal(signal.times, original_times)
+        self.assertEqual(signal.sampling_period, original_period)
+
+    def test__nested_slices_preserve_sample_times(self):
+        signal = AnalogSignal(np.arange(20), units="mV", sampling_rate=4 * pq.Hz, t_start=2 * pq.s)
+        result = signal[1::2][-3:]
+        assert_array_equal(result.magnitude, signal.magnitude[1::2][-3:])
+        assert_array_equal(result.times, signal.times[1::2][-3:])
+
     def test__index_dim1_and_slice_dim0_should_return_single_channel_analogsignal(self):
         result = self.signal1[2:7, 0]
         self.assertIsInstance(result, AnalogSignal)