Repository: Project-MONAI/MONAI

Issue:
`OneOf.inverse`  for the metatensors
this is a feature request to extend the inverse of `OneOf` which currently supports only mapping type input:
https://github.com/Project-MONAI/MONAI/blob/ca90628ffbadf37031b06d2506c7938c0a29f25b/monai/transforms/compose.py#L266-L267


Discussion:

Resolving patch:
diff --git a/monai/transforms/compose.py b/monai/transforms/compose.py
--- a/monai/transforms/compose.py
+++ b/monai/transforms/compose.py
@@ -17,6 +17,7 @@
 
 import numpy as np
 
+import monai
 from monai.transforms.inverse import InvertibleTransform
 
 # For backwards compatibility (so this still works: from monai.transforms.compose import MapTransform)
@@ -254,26 +255,27 @@ def __call__(self, data):
         _transform = self.transforms[index]
         data = apply_transform(_transform, data, self.map_items, self.unpack_items, self.log_stats)
         # if the data is a mapping (dictionary), append the OneOf transform to the end
-        if isinstance(data, Mapping):
-            for key in data.keys():
-                if self.trace_key(key) in data:
+        if isinstance(data, monai.data.MetaTensor):
+            self.push_transform(data, extra_info={"index": index})
+        elif isinstance(data, Mapping):
+            for key in data:  # dictionary not change size during iteration
+                if isinstance(data[key], monai.data.MetaTensor) or self.trace_key(key) in data:
                     self.push_transform(data, key, extra_info={"index": index})
         return data
 
     def inverse(self, data):
         if len(self.transforms) == 0:
             return data
-        if not isinstance(data, Mapping):
-            raise RuntimeError("Inverse only implemented for Mapping (dictionary) data")
 
-        # loop until we get an index and then break (since they'll all be the same)
         index = None
-        for key in data.keys():
-            if self.trace_key(key) in data:
-                # get the index of the applied OneOf transform
-                index = self.get_most_recent_transform(data, key)[TraceKeys.EXTRA_INFO]["index"]
-                # and then remove the OneOf transform
-                self.pop_transform(data, key)
+        if isinstance(data, monai.data.MetaTensor):
+            index = self.pop_transform(data)[TraceKeys.EXTRA_INFO]["index"]
+        elif isinstance(data, Mapping):
+            for key in data:
+                if isinstance(data[key], monai.data.MetaTensor) or self.trace_key(key) in data:
+                    index = self.pop_transform(data, key)[TraceKeys.EXTRA_INFO]["index"]
+        else:
+            raise RuntimeError("Inverse only implemented for Mapping (dictionary) or MetaTensor data.")
         if index is None:
             # no invertible transforms have been applied
             return data


Test patch:
diff --git a/tests/test_one_of.py b/tests/test_one_of.py
--- a/tests/test_one_of.py
+++ b/tests/test_one_of.py
@@ -15,11 +15,15 @@
 import numpy as np
 from parameterized import parameterized
 
+from monai.data import MetaTensor
 from monai.transforms import (
     InvertibleTransform,
     OneOf,
+    RandScaleIntensity,
     RandScaleIntensityd,
+    RandShiftIntensity,
     RandShiftIntensityd,
+    Resize,
     Resized,
     TraceableTransform,
     Transform,
@@ -106,10 +110,10 @@ def __init__(self, keys):
 
 KEYS = ["x", "y"]
 TEST_INVERSES = [
-    (OneOf((InvA(KEYS), InvB(KEYS))), True),
-    (OneOf((OneOf((InvA(KEYS), InvB(KEYS))), OneOf((InvB(KEYS), InvA(KEYS))))), True),
-    (OneOf((Compose((InvA(KEYS), InvB(KEYS))), Compose((InvB(KEYS), InvA(KEYS))))), True),
-    (OneOf((NonInv(KEYS), NonInv(KEYS))), False),
+    (OneOf((InvA(KEYS), InvB(KEYS))), True, True),
+    (OneOf((OneOf((InvA(KEYS), InvB(KEYS))), OneOf((InvB(KEYS), InvA(KEYS))))), True, False),
+    (OneOf((Compose((InvA(KEYS), InvB(KEYS))), Compose((InvB(KEYS), InvA(KEYS))))), True, False),
+    (OneOf((NonInv(KEYS), NonInv(KEYS))), False, False),
 ]
 
 
@@ -148,13 +152,17 @@ def _match(a, b):
         _match(p, f)
 
     @parameterized.expand(TEST_INVERSES)
-    def test_inverse(self, transform, invertible):
-        data = {k: (i + 1) * 10.0 for i, k in enumerate(KEYS)}
+    def test_inverse(self, transform, invertible, use_metatensor):
+        data = {k: (i + 1) * 10.0 if not use_metatensor else MetaTensor((i + 1) * 10.0) for i, k in enumerate(KEYS)}
         fwd_data = transform(data)
 
         if invertible:
             for k in KEYS:
-                t = fwd_data[TraceableTransform.trace_key(k)][-1]
+                t = (
+                    fwd_data[TraceableTransform.trace_key(k)][-1]
+                    if not use_metatensor
+                    else fwd_data[k].applied_operations[-1]
+                )
                 # make sure the OneOf index was stored
                 self.assertEqual(t[TraceKeys.CLASS_NAME], OneOf.__name__)
                 # make sure index exists and is in bounds
@@ -166,9 +174,11 @@ def test_inverse(self, transform, invertible):
         if invertible:
             for k in KEYS:
                 # check transform was removed
-                self.assertTrue(
-                    len(fwd_inv_data[TraceableTransform.trace_key(k)]) < len(fwd_data[TraceableTransform.trace_key(k)])
-                )
+                if not use_metatensor:
+                    self.assertTrue(
+                        len(fwd_inv_data[TraceableTransform.trace_key(k)])
+                        < len(fwd_data[TraceableTransform.trace_key(k)])
+                    )
                 # check data is same as original (and different from forward)
                 self.assertEqual(fwd_inv_data[k], data[k])
                 self.assertNotEqual(fwd_inv_data[k], fwd_data[k])
@@ -186,15 +196,34 @@ def test_inverse_compose(self):
                         RandShiftIntensityd(keys="img", offsets=0.5, prob=1.0),
                     ]
                 ),
+                OneOf(
+                    [
+                        RandScaleIntensityd(keys="img", factors=0.5, prob=1.0),
+                        RandShiftIntensityd(keys="img", offsets=0.5, prob=1.0),
+                    ]
+                ),
             ]
         )
         transform.set_random_state(seed=0)
         result = transform({"img": np.ones((1, 101, 102, 103))})
-
         result = transform.inverse(result)
         # invert to the original spatial shape
         self.assertTupleEqual(result["img"].shape, (1, 101, 102, 103))
 
+    def test_inverse_metatensor(self):
+        transform = Compose(
+            [
+                Resize(spatial_size=[100, 100, 100]),
+                OneOf([RandScaleIntensity(factors=0.5, prob=1.0), RandShiftIntensity(offsets=0.5, prob=1.0)]),
+                OneOf([RandScaleIntensity(factors=0.5, prob=1.0), RandShiftIntensity(offsets=0.5, prob=1.0)]),
+            ]
+        )
+        transform.set_random_state(seed=0)
+        result = transform(np.ones((1, 101, 102, 103)))
+        self.assertTupleEqual(result.shape, (1, 100, 100, 100))
+        result = transform.inverse(result)
+        self.assertTupleEqual(result.shape, (1, 101, 102, 103))
+
     def test_one_of(self):
         p = OneOf((A(), B(), C()), (1, 2, 1))
         counts = [0] * 3