Add start_index property to DigitalWaveform and NumericWaveform (#194)

* feat: add start_index property to DigitalWaveform and NumericWaveform classes

* add start_index for spectrum also

* fix comment

---------

Co-authored-by: Mike Prosser <[email protected]>

Author: mikeprosserni

src/nitypes/waveform/_digital/_waveform.py

@@ -922,6 +922,11 @@ def signal_count(self) -> int:
         shape: tuple[int, ...] = self._data.shape
         return shape[1]
 
+    @property
+    def start_index(self) -> int:
+        """The sample index of the underlying array at which the waveform data begins."""
+        return self._start_index
+
     @property
     def capacity(self) -> int:
         """The total capacity available for waveform data.

src/nitypes/waveform/_numeric.py

@@ -466,6 +466,11 @@ def sample_count(self, value: int) -> None:
             )
         self._sample_count = value
 
+    @property
+    def start_index(self) -> int:
+        """The sample index of the underlying array at which the waveform data begins."""
+        return self._start_index
+
     @property
     def capacity(self) -> int:
         """The total capacity available for waveform data.

src/nitypes/waveform/_spectrum.py

@@ -542,6 +542,11 @@ def sample_count(self) -> int:
         """The number of samples in the spectrum."""
         return self._sample_count
 
+    @property
+    def start_index(self) -> int:
+        """The sample index of the underlying array at which the spectrum data begins."""
+        return self._start_index
+
     @property
     def capacity(self) -> int:
         """The total capacity available for spectrum data.

tests/unit/waveform/test_analog_waveform.py

@@ -580,6 +580,7 @@ def test___array_subset___from_array_2d___creates_waveform_with_array_subset(
     assert len(waveforms) == 2
     for i in range(len(waveforms)):
         assert waveforms[i].raw_data.tolist() == expected_data[i]
+        assert waveforms[i].start_index == (start_index if start_index is not None else 0)
 
 
 @pytest.mark.parametrize(
@@ -1595,13 +1596,13 @@ def test___waveform_with_start_index___load_data___clears_start_index() -> None:
     waveform = AnalogWaveform.from_array_1d(
         np.array([0, 1, 2], np.int32), np.int32, copy=False, start_index=1, sample_count=1
     )
-    assert waveform._start_index == 1
+    assert waveform.start_index == 1
     array = np.array([3], np.int32)
 
     waveform.load_data(array)
 
     assert list(waveform.raw_data) == [3]
-    assert waveform._start_index == 0
+    assert waveform.start_index == 0
 
 
 def test___ndarray_subset___load_data___overwrites_data() -> None:
@@ -1611,7 +1612,7 @@ def test___ndarray_subset___load_data___overwrites_data() -> None:
     waveform.load_data(array, start_index=1, sample_count=1)
 
     assert list(waveform.raw_data) == [4]
-    assert waveform._start_index == 0
+    assert waveform.start_index == 0
     assert waveform.capacity == 3
 
 

tests/unit/waveform/test_digital_waveform.py

@@ -321,6 +321,7 @@ def test___array_subset___from_port___creates_waveform_with_array_subset() -> No
 
     waveform = DigitalWaveform.from_port(array, start_index=2, sample_count=4)
 
+    assert waveform.start_index == 2
     assert waveform.sample_count == 4
     assert waveform.signal_count == 8
     assert waveform.data.tolist() == [
@@ -448,11 +449,13 @@ def test___array_subset___from_ports___creates_waveform_with_array_subset() -> N
     waveforms = DigitalWaveform.from_ports(array, start_index=1, sample_count=1)
 
     assert len(waveforms) == 2
+    assert waveforms[0].start_index == 1
     assert waveforms[0].sample_count == 1
     assert waveforms[0].signal_count == 8
     assert waveforms[0].data.tolist() == [
         [1, 0, 0, 0, 0, 0, 0, 0],
     ]
+    assert waveforms[1].start_index == 1
     assert waveforms[1].sample_count == 1
     assert waveforms[1].signal_count == 8
     assert waveforms[1].data.tolist() == [
@@ -1270,13 +1273,13 @@ def test___waveform_with_start_index___load_data___clears_start_index() -> None:
     waveform = DigitalWaveform.from_lines(
         np.array([[0], [1], [2]], np.uint8), np.uint8, copy=False, start_index=1, sample_count=1
     )
-    assert waveform._start_index == 1
+    assert waveform.start_index == 1
     array = np.array([[3]], np.uint8)
 
     waveform.load_data(array)
 
     assert waveform.data.tolist() == [[3]]
-    assert waveform._start_index == 0
+    assert waveform.start_index == 0
 
 
 def test___ndarray_subset___load_data___overwrites_data() -> None:
@@ -1286,7 +1289,7 @@ def test___ndarray_subset___load_data___overwrites_data() -> None:
     waveform.load_data(array, start_index=1, sample_count=1)
 
     assert waveform.data.tolist() == [[4]]
-    assert waveform._start_index == 0
+    assert waveform.start_index == 0
     assert waveform.capacity == 3
 
 

tests/unit/waveform/test_spectrum.py

@@ -1071,13 +1071,13 @@ def test___spectrum_with_start_index___load_data___clears_start_index() -> None:
     spectrum = Spectrum.from_array_1d(
         np.array([0, 1, 2], np.int32), np.int32, copy=False, start_index=1, sample_count=1
     )
-    assert spectrum._start_index == 1
+    assert spectrum.start_index == 1
     array = np.array([3], np.int32)
 
     spectrum.load_data(array)
 
     assert list(spectrum.data) == [3]
-    assert spectrum._start_index == 0
+    assert spectrum.start_index == 0
 
 
 def test___ndarray_subset___load_data___overwrites_data() -> None:
@@ -1087,7 +1087,7 @@ def test___ndarray_subset___load_data___overwrites_data() -> None:
     spectrum.load_data(array, start_index=1, sample_count=1)
 
     assert list(spectrum.data) == [4]
-    assert spectrum._start_index == 0
+    assert spectrum.start_index == 0
     assert spectrum.capacity == 3