Add optional parameter to trim method for shifting

start times

fortepyan/midi/structures.py

@@ -57,7 +57,7 @@ def time_shift(self, shift_s: float):
         self.df.start += shift_s
         self.df.end += shift_s
 
-    def trim(self, start: float, finish: float) -> "MidiPiece":
+    def trim(self, start: float, finish: float, shift_time: bool = True) -> "MidiPiece":
         """Trim the MidiPiece object between the specified start and finish time.
 
         This function takes two parameters, `start` and `finish`, which represent the start and end time in seconds,
@@ -78,9 +78,11 @@ def trim(self, start: float, finish: float) -> "MidiPiece":
         # Get the start and end indices for the new MidiPiece object
         start = idxs[0]
         finish = idxs[-1] + 1
+        # Create a slice object to pass to __getitem__
+        slice_obj = slice(start, finish)
         # Slice the original MidiPiece object to create the trimmed MidiPiece object
-        out = self[start:finish]
-        # Return the trimmed MidiPiece object
+        out = self.__getitem__(slice_obj, shift_time)
+
         return out
 
     def __sanitize_get_index(self, index: slice) -> slice:
@@ -97,19 +99,26 @@ def __sanitize_get_index(self, index: slice) -> slice:
 
         return index
 
-    def __getitem__(self, index: slice) -> "MidiPiece":
+    def __getitem__(self, index: slice, shift_time: bool = True) -> "MidiPiece":
         index = self.__sanitize_get_index(index)
         part = self.df[index].reset_index(drop=True)
 
-        first_sound = part.start.min()
-        part.start -= first_sound
-        part.end -= first_sound
+        if shift_time:
+            # Shift the start and end times so that the first note starts at 0
+            first_sound = part.start.min()
+            part.start -= first_sound
+            part.end -= first_sound
+            # Adjust the source to reflect the new start time
+            start_time_adjustment = first_sound
+        else:
+            # No adjustment to the start time
+            start_time_adjustment = 0
 
-        # Make sure the piece can always be track back to the original file exactly
+        # Make sure the piece can always be tracked back to the original file exactly
         out_source = dict(self.source)
         out_source["start"] = self.source.get("start", 0) + index.start
         out_source["finish"] = self.source.get("start", 0) + index.stop
-        out_source["start_time"] = self.source.get("start_time", 0) + first_sound
+        out_source["start_time"] = self.source.get("start_time", 0) + start_time_adjustment
         out = MidiPiece(df=part, source=out_source)
 
         return out

tests/midi/test_structures.py

@@ -73,7 +73,7 @@ def test_midi_piece_duration_calculation(sample_df):
     assert piece.duration == 5.5
 
 
-def test_trim_within_bounds(sample_midi_piece):
+def test_trim_within_bounds_with_shift(sample_midi_piece):
     # Test currently works as in the original code.
     # We might want to change this behavior so that
     # we do not treat the trimed piece as a new piece
@@ -84,6 +84,16 @@ def test_trim_within_bounds(sample_midi_piece):
     assert trimmed_piece.df["end"].iloc[-1] == 2, "New last note should end at 2 seconds."
 
 
+def test_trim_within_bounds_no_shift(sample_midi_piece):
+    # This test should not shift the start times
+    trimmed_piece = sample_midi_piece.trim(2, 3, shift_time=False)
+    assert len(trimmed_piece.df) == 2, "Trimmed MidiPiece should contain 2 notes."
+    # Since we're not shifting, the start should not be 0 but the actual start time
+    assert trimmed_piece.df["start"].iloc[0] == 2, "First note should retain its original start time."
+    assert trimmed_piece.df["pitch"].iloc[0] == 64, "First note should have pitch 64."
+    assert trimmed_piece.df["end"].iloc[-1] == 4, "Last note should end at 4 seconds."
+
+
 def test_trim_at_boundaries(sample_midi_piece):
     trimmed_piece = sample_midi_piece.trim(0, 5.5)
     assert trimmed_piece.size == sample_midi_piece.size, "Trimming at boundaries should not change the size."