Fix multilabel_accuracy of MixedHLabelAccuracy (#4042)

* Fix metric for multi-label

* Fix1

* Add CHANGELOG

CHANGELOG.md

@@ -86,6 +86,8 @@ All notable changes to this project will be documented in this file.
   (<https://github.com/openvinotoolkit/training_extensions/pull/4014>)
 - Fix out_features in HierarchicalCBAMClsHead
   (<https://github.com/openvinotoolkit/training_extensions/pull/4016>)
+- Fix multilabel_accuracy of MixedHLabelAccuracy
+  (<https://github.com/openvinotoolkit/training_extensions/pull/4042>)
 
 ## \[v2.1.0\]
 

src/otx/core/metrics/accuracy.py

@@ -288,12 +288,17 @@ def __init__(
         ]
 
         # Multilabel classification accuracy metrics
-        if self.num_multilabel_classes > 0:
+        # https://github.com/Lightning-AI/torchmetrics/blob/6377aa5b6fe2863761839e6b8b5a857ef1b8acfa/src/torchmetrics/functional/classification/stat_scores.py#L583-L584
+        # MultilabelAccuracy is available when num_multilabel_classes is greater than 2.
+        self.multilabel_accuracy = None
+        if self.num_multilabel_classes > 1:
             self.multilabel_accuracy = TorchmetricMultilabelAcc(
                 num_labels=self.num_multilabel_classes,
                 threshold=0.5,
                 average="macro",
             )
+        elif self.num_multilabel_classes == 1:
+            self.multilabel_accuracy = TorchmetricAcc(task="binary", num_classes=self.num_multilabel_classes)
 
     def _apply(self, fn: Callable, exclude_state: Sequence[str] = "") -> nn.Module:
         self.multiclass_head_accuracy = [
@@ -303,7 +308,7 @@ def _apply(self, fn: Callable, exclude_state: Sequence[str] = "") -> nn.Module:
             )
             for acc in self.multiclass_head_accuracy
         ]
-        if self.num_multilabel_classes > 0:
+        if self.multilabel_accuracy is not None:
             self.multilabel_accuracy = self.multilabel_accuracy._apply(fn, exclude_state)  # noqa: SLF001
         return self
 
@@ -322,7 +327,7 @@ def update(self, preds: torch.Tensor, target: torch.Tensor) -> None:
                     target_multiclass[multiclass_mask],
                 )
 
-        if self.num_multilabel_classes > 0:
+        if self.multilabel_accuracy is not None:
             # Split preds into multiclass and multilabel parts
             preds_multilabel = preds[:, self.num_multiclass_heads :]
             target_multilabel = target[:, self.num_multiclass_heads :]
@@ -337,7 +342,7 @@ def compute(self) -> torch.Tensor:
             ),
         )
 
-        if self.num_multilabel_classes > 0:
+        if self.multilabel_accuracy is not None:
             multilabel_acc = self.multilabel_accuracy.compute()
 
             return (multiclass_accs + multilabel_acc) / 2

tests/unit/core/metrics/test_accuracy.py

@@ -13,7 +13,7 @@
     MultilabelAccuracywithLabelGroup,
 )
 from otx.core.types.label import HLabelInfo, LabelInfo
-from torchmetrics.classification.accuracy import BinaryAccuracy, MulticlassAccuracy
+from torchmetrics.classification.accuracy import BinaryAccuracy, MulticlassAccuracy, MultilabelAccuracy
 
 
 class TestAccuracy:
@@ -120,3 +120,28 @@ def test_multilabel_only(self) -> None:
                 head_logits_info={"head1": (0, 5), "head2": (5, 10)},
                 threshold_multilabel=0.5,
             )
+
+    def test_multilabel_accuracy(self, hlabel_accuracy) -> None:
+        # Normal Case: num_multilabel_classes > 1 -> MultilabelAccuracy
+        assert hlabel_accuracy.num_multilabel_classes == 3
+        assert isinstance(hlabel_accuracy.multilabel_accuracy, MultilabelAccuracy)
+
+        # Edge Case: num_multilabel_classes = 1 -> BinaryAccuracy
+        acc = MixedHLabelAccuracy(
+            num_multiclass_heads=2,
+            num_multilabel_classes=1,
+            head_logits_info={"head1": (0, 5), "head2": (5, 10)},
+            threshold_multilabel=0.5,
+        )
+        assert acc.num_multilabel_classes == 1
+        assert isinstance(acc.multilabel_accuracy, BinaryAccuracy)
+
+        # None Case: num_multilabel_classes = 0 -> None
+        acc = MixedHLabelAccuracy(
+            num_multiclass_heads=2,
+            num_multilabel_classes=0,
+            head_logits_info={"head1": (0, 5), "head2": (5, 10)},
+            threshold_multilabel=0.5,
+        )
+        assert acc.num_multilabel_classes == 0
+        assert acc.multilabel_accuracy is None