179 add DeleteKeys transform (#180)

* [DLMED] add DeleteKeys transform

* [DLMED] remove unnecessary copy

monai/transforms/composables.py

@@ -883,3 +883,25 @@ def __call__(self, data):
         for key in self.keys:
             d[key] = zoomer(d[key])
         return d
+
+
+@export
+@alias('DeleteKeysD', 'DeleteKeysDict')
+class DeleteKeysd(MapTransform):
+    """
+    Delete specified keys from data dictionary to release memory.
+    It will remove the key-values and copy the others to construct a new dictionary.
+    """
+
+    def __init__(self, keys):
+        """
+        Args:
+            keys (hashable items): keys of the corresponding items to be transformed.
+                See also: monai.transform.composables.MapTransform
+        """
+        MapTransform.__init__(self, keys)
+
+    def __call__(self, data):
+        for key in self.keys:
+            del data[key]
+        return dict(data)

tests/test_delete_keys.py

@@ -0,0 +1,38 @@
+# Copyright 2020 MONAI Consortium
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#     http://www.apache.org/licenses/LICENSE-2.0
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# 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 unittest
+import time
+import sys
+from parameterized import parameterized
+from monai.transforms.composables import DeleteKeysd
+
+TEST_CASE_1 = [
+    {'keys': [str(i) for i in range(30)]},
+    20,
+    648,
+]
+
+
+class TestDeleteKeysd(unittest.TestCase):
+
+    @parameterized.expand([TEST_CASE_1])
+    def test_memory(self, input_param, expected_key_size, expected_mem_size):
+        input_data = dict()
+        for i in range(50):
+            input_data[str(i)] = [time.time()] * 100000
+        result = DeleteKeysd(**input_param)(input_data)
+        self.assertEqual(len(result.keys()), expected_key_size)
+        self.assertEqual(sys.getsizeof(result), expected_mem_size)
+
+
+if __name__ == '__main__':
+    unittest.main()