From f531ab86df58028da59b33be409684b2eb69cdd7 Mon Sep 17 00:00:00 2001
From: Mohammad Adil <madil@nvidia.com>
Date: Fri, 6 Mar 2020 15:34:12 -0800
Subject: [PATCH] Adding RandomFlip.

---
 monai/transforms/transforms.py | 31 ++++++++++++++++++------
 tests/test_random_flip.py      | 44 ++++++++++++++++++++++++++++++++++
 2 files changed, 68 insertions(+), 7 deletions(-)
 create mode 100644 tests/test_random_flip.py

diff --git a/monai/transforms/transforms.py b/monai/transforms/transforms.py
index fb1bf468d6..f35a072c29 100644
--- a/monai/transforms/transforms.py
+++ b/monai/transforms/transforms.py
@@ -441,10 +441,27 @@ def __call__(self, img):
         return data
 
 
-# if __name__ == "__main__":
-#     img = np.array((1, 2, 3, 4)).reshape((1, 2, 2))
-#     rotator = RandRotate90(prob=0.0, max_k=3, axes=(1, 2))
-#     # rotator.set_random_state(1234)
-#     img_result = rotator(img)
-#     print(type(img))
-#     print(img_result)
+@export
+class RandomFlip(Randomizable):
+    """Randomly flips the image along axes.
+
+    Args:
+        prob (float): Probability of flipping.
+        axes (None, int or tuple of ints): Axes along which to flip over. Default is None.
+    """
+
+    def __init__(self, prob=0.1, axis=None):
+        self.axis = axis
+        self.prob = prob
+
+        self._do_transform = False
+
+    def randomize(self):
+        self._do_transform = self.R.random_sample() < self.prob
+
+    def __call__(self, img):
+        self.randomize()
+        if not self._do_transform:
+            return img
+        flipper = Flip(axis=self.axis)
+        return flipper(img)
diff --git a/tests/test_random_flip.py b/tests/test_random_flip.py
new file mode 100644
index 0000000000..ec95485f20
--- /dev/null
+++ b/tests/test_random_flip.py
@@ -0,0 +1,44 @@
+# 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 numpy as np
+from parameterized import parameterized
+
+from monai.transforms import RandomFlip
+from tests.utils import NumpyImageTestCase2D
+
+
+class RandomFlipTest(NumpyImageTestCase2D):
+
+    @parameterized.expand([
+        ("wrong_axis", ['s', 1], TypeError),
+        ("not_numbers", 's', AssertionError)
+    ])
+    def test_invalid_inputs(self, _, axis, raises):
+        with self.assertRaises(raises):
+            flip = RandomFlip(prob=1.0, axis=axis)
+            flip(self.imt)
+
+    @parameterized.expand([
+        ("no_axis", None),
+        ("one_axis", 1),
+        ("many_axis", [0, 1, 2])
+    ])
+    def test_correct_results(self, _, axis):
+        flip = RandomFlip(prob=1.0, axis=axis)
+        expected = np.flip(self.imt, axis)
+        self.assertTrue(np.allclose(expected, flip(self.imt)))
+
+
+if __name__ == '__main__':
+    unittest.main()