➕ Add Detections.merge method

supervision/detection/core.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from dataclasses import dataclass
+from dataclasses import astuple, dataclass
 from typing import Any, Iterator, List, Optional, Tuple
 
 import numpy as np
@@ -363,6 +363,55 @@ def empty(cls) -> Detections:
             class_id=np.array([], dtype=int),
         )
 
+    @classmethod
+    def merge(cls, detections_list: List[Detections]) -> Detections:
+        """
+        Merge a list of Detections objects into a single Detections object.
+
+        This method takes a list of Detections objects and combines their respective fields (`xyxy`, `mask`,
+        `confidence`, `class_id`, and `tracker_id`) into a single Detections object. If all elements in a field are not
+        `None`, the corresponding field will be stacked. Otherwise, the field will be set to `None`.
+
+        Args:
+            detections_list (List[Detections]): A list of Detections objects to merge.
+
+        Returns:
+            (Detections): A single Detections object containing the merged data from the input list.
+
+        Example:
+            ```python
+            >>> from supervision import Detections
+
+            >>> detections_1 = Detections(...)
+            >>> detections_2 = Detections(...)
+
+            >>> merged_detections = Detections.merge([detections_1, detections_2])
+            ```
+        """
+        if len(detections_list) == 0:
+            return Detections.empty()
+
+        detections_tuples_list = [astuple(detection) for detection in detections_list]
+        xyxy, mask, confidence, class_id, tracker_id = [
+            list(field) for field in zip(*detections_tuples_list)
+        ]
+
+        all_not_none = lambda l: all(x is not None for x in l)
+
+        xyxy = np.vstack(xyxy)
+        mask = np.vstack(mask) if all_not_none(mask) else None
+        confidence = np.hstack(confidence) if all_not_none(confidence) else None
+        class_id = np.hstack(class_id) if all_not_none(class_id) else None
+        tracker_id = np.hstack(tracker_id) if all_not_none(tracker_id) else None
+
+        return cls(
+            xyxy=xyxy,
+            mask=mask,
+            confidence=confidence,
+            class_id=class_id,
+            tracker_id=tracker_id,
+        )
+
     def get_anchor_coordinates(self, anchor: Position) -> np.ndarray:
         """
         Returns the bounding box coordinates for a specific anchor.

test/detection/test_core.py

@@ -4,7 +4,7 @@
 
 from supervision import Detections
 
-from typing import Optional, Union
+from typing import Optional, Union, List
 
 import numpy as np
 
@@ -35,6 +35,15 @@
     ], dtype=np.float32)
 
 
+def mock_detections(xyxy, confidence = None, class_id = None, tracker_id = None) -> Detections:
+    return Detections(
+        xyxy = np.array(xyxy, dtype=np.float32),
+        confidence = confidence if confidence is None else np.array(confidence, dtype=np.float32),
+        class_id = class_id if class_id is None else np.array(class_id, dtype=int),
+        tracker_id = tracker_id if tracker_id is None else np.array(tracker_id, dtype=int),
+    )
+
+
 @pytest.mark.parametrize(
     'detections, index, expected_result, exception',
     [
@@ -103,3 +112,90 @@ def test_getitem(
     with exception:
         result = detections[index]
         assert result == expected_result
+
+
+@pytest.mark.parametrize(
+    'detections_list, expected_result, exception',
+    [
+        (
+            [],
+            Detections.empty(),
+            DoesNotRaise()
+        ),  # empty detections list
+        (
+            [
+                Detections.empty()
+            ],
+            Detections.empty(),
+            DoesNotRaise()
+        ),  # single empty detections
+        (
+            [
+                mock_detections(xyxy=[[10, 10, 20, 20]])
+            ],
+            mock_detections(xyxy=[[10, 10, 20, 20]]),
+            DoesNotRaise()
+        ),  # single detection with xyxy field
+        (
+            [
+                mock_detections(xyxy=[[10, 10, 20, 20]]),
+                Detections.empty()
+            ],
+            mock_detections(xyxy=[[10, 10, 20, 20]]),
+            DoesNotRaise()
+        ),  # single detection with xyxy field + empty detection
+        (
+            [
+                mock_detections(xyxy=[[10, 10, 20, 20]]),
+                mock_detections(xyxy=[[20, 20, 30, 30]])
+            ],
+            mock_detections(
+                xyxy=[
+                    [10, 10, 20, 20],
+                    [20, 20, 30, 30]
+                ]),
+            DoesNotRaise()
+        ),  # two detections with xyxy field
+        (
+            [
+                mock_detections(
+                    xyxy=[[10, 10, 20, 20]],
+                    class_id=[0]),
+                mock_detections(
+                    xyxy=[[20, 20, 30, 30]])
+            ],
+            mock_detections(
+                xyxy=[
+                    [10, 10, 20, 20],
+                    [20, 20, 30, 30]
+                ]),
+            DoesNotRaise()
+        ),  # detection with xyxy, class_id fields + detection with xyxy field
+(
+            [
+                mock_detections(
+                    xyxy=[[10, 10, 20, 20]],
+                    class_id=[0]),
+                mock_detections(
+                    xyxy=[[20, 20, 30, 30]],
+                    class_id=[1]),
+            ],
+            mock_detections(
+                xyxy=[
+                    [10, 10, 20, 20],
+                    [20, 20, 30, 30]
+                ],
+                class_id=[0, 1]
+            ),
+            DoesNotRaise()
+        ),  # two detections with xyxy, class_id fields
+    ]
+)
+def test_merge(
+        detections_list: List[Detections],
+        expected_result: Optional[Detections],
+        exception: Exception
+) -> None:
+    with exception:
+        result = Detections.merge(detections_list=detections_list)
+        assert result == expected_result