5414 size/size() for metatensor compatibility (#5415)

Signed-off-by: Wenqi Li <[email protected]>

Fixes #5414



### Types of changes
<!--- Put an `x` in all the boxes that apply, and remove the not
applicable items -->
- [x] Non-breaking change (fix or new feature that would not break
existing functionality).
- [ ] Breaking change (fix or new feature that would cause existing
functionality to change).
- [x] New tests added to cover the changes.
- [ ] Integration tests passed locally by running `./runtests.sh -f -u
--net --coverage`.
- [ ] Quick tests passed locally by running `./runtests.sh --quick
--unittests --disttests`.
- [ ] In-line docstrings updated.
- [ ] Documentation updated, tested `make html` command in the `docs/`
folder.

Signed-off-by: Wenqi Li <[email protected]>
Signed-off-by: KumoLiu <[email protected]>

Author: wyli

monai/transforms/utils.py

@@ -505,11 +505,11 @@ def generate_pos_neg_label_crop_centers(
         raise ValueError("No sampling location available.")
 
     if len(fg_indices) == 0 or len(bg_indices) == 0:
+        pos_ratio = 0 if len(fg_indices) == 0 else 1
         warnings.warn(
-            f"N foreground {len(fg_indices)}, N  background {len(bg_indices)},"
-            "unable to generate class balanced samples."
+            f"Num foregrounds {len(fg_indices)}, Num backgrounds {len(bg_indices)}, "
+            f"unable to generate class balanced samples, setting `pos_ratio` to {pos_ratio}."
         )
-        pos_ratio = 0 if fg_indices.size == 0 else 1
 
     for _ in range(num_samples):
         indices_to_use = fg_indices if rand_state.rand() < pos_ratio else bg_indices

tests/test_generate_pos_neg_label_crop_centers.py

@@ -31,7 +31,20 @@
         list,
         2,
         3,
-    ]
+    ],
+    [
+        {
+            "spatial_size": [2, 2, 2],
+            "num_samples": 2,
+            "pos_ratio": 0.0,
+            "label_spatial_shape": [3, 3, 3],
+            "fg_indices": [],
+            "bg_indices": [3, 12, 21],
+        },
+        list,
+        2,
+        3,
+    ],
 ]