fix: MetricCollection did not copy the inner state of the metric in…

… `ClasswiseWrapper` when computing group metrics (#2390)

* fix: MetricCollection did not copy inner state of metric in ClasswiseWrapper when computing groups metrics

Issue Link: #2389

* fix: set _persistent and _reductions be same as internal metric

* test: check metric state_dict wrapped in `ClasswiseWrapper`

---------

Co-authored-by: Jirka Borovec <[email protected]>
(cherry picked from commit 1951a06)

src/torchmetrics/wrappers/classwise.py

@@ -11,6 +11,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+import typing
 from typing import Any, Dict, List, Optional, Sequence, Union
 
 from torch import Tensor
@@ -20,6 +21,9 @@
 from torchmetrics.utilities.plot import _AX_TYPE, _PLOT_OUT_TYPE
 from torchmetrics.wrappers.abstract import WrapperMetric
 
+if typing.TYPE_CHECKING:
+    from torch.nn import Module
+
 if not _MATPLOTLIB_AVAILABLE:
     __doctest_skip__ = ["ClasswiseWrapper.plot"]
 
@@ -209,3 +213,22 @@ def plot(
 
         """
         return self._plot(val, ax)
+
+    def __getattr__(self, name: str) -> Union[Tensor, "Module"]:
+        """Get attribute from classwise wrapper."""
+        # return state from self.metric
+        if name in ["tp", "fp", "fn", "tn"]:
+            return getattr(self.metric, name)
+
+        return super().__getattr__(name)
+
+    def __setattr__(self, name: str, value: Any) -> None:
+        """Set attribute to classwise wrapper."""
+        super().__setattr__(name, value)
+        if name == "metric":
+            self._defaults = self.metric._defaults
+            self._persistent = self.metric._persistent
+            self._reductions = self.metric._reductions
+        if hasattr(self, "metric") and name in ["tp", "fp", "fn", "tn", "_update_count", "_computed"]:
+            # update ``_update_count`` and ``_computed`` of internal metric to prevent warning.
+            setattr(self.metric, name, value)

tests/unittests/bases/test_collections.py

@@ -17,7 +17,7 @@
 
 import pytest
 import torch
-from torchmetrics import Metric, MetricCollection
+from torchmetrics import ClasswiseWrapper, Metric, MetricCollection
 from torchmetrics.classification import (
     BinaryAccuracy,
     MulticlassAccuracy,
@@ -540,6 +540,44 @@ def test_compute_group_define_by_user():
     assert m.compute()
 
 
+def test_classwise_wrapper_compute_group():
+    """Check that user can provide compute groups."""
+    classwise_accuracy = ClasswiseWrapper(MulticlassAccuracy(num_classes=3, average=None), prefix="accuracy")
+    classwise_recall = ClasswiseWrapper(MulticlassRecall(num_classes=3, average=None), prefix="recall")
+    classwise_precision = ClasswiseWrapper(MulticlassPrecision(num_classes=3, average=None), prefix="precision")
+
+    m = MetricCollection(
+        {
+            "accuracy": ClasswiseWrapper(MulticlassAccuracy(num_classes=3, average=None), prefix="accuracy"),
+            "recall": ClasswiseWrapper(MulticlassRecall(num_classes=3, average=None), prefix="recall"),
+            "precision": ClasswiseWrapper(MulticlassPrecision(num_classes=3, average=None), prefix="precision"),
+        },
+        compute_groups=[["accuracy", "recall", "precision"]],
+    )
+
+    # Check that we are not going to check the groups in the first update
+    assert m._groups_checked
+    assert m.compute_groups == {0: ["accuracy", "recall", "precision"]}
+
+    preds = torch.randn(10, 3).softmax(dim=-1)
+    target = torch.randint(3, (10,))
+
+    expected = {
+        **classwise_accuracy(preds, target),
+        **classwise_recall(preds, target),
+        **classwise_precision(preds, target),
+    }
+
+    m.update(preds, target)
+    res = m.compute()
+
+    for key in expected:
+        assert torch.allclose(res[key], expected[key])
+
+    # check metric state_dict
+    m.state_dict()
+
+
 def test_compute_on_different_dtype():
     """Check that extraction of compute groups are robust towards difference in dtype."""
     m = MetricCollection([