Implement min, max, sum and mean of Rolling in Series and DataFrame

databricks/koalas/generic.py

@@ -1393,8 +1393,9 @@ def median(self, accuracy=10000):
         # This is expected to be small so it's fine to transpose.
         return DataFrame(sdf)._to_internal_pandas().transpose().iloc[:, 0]
 
-    def rolling(self, *args, **kwargs):
-        return Rolling(self)
+    # TODO: 'center', 'win_type', 'on', 'axis' parameter should be implemented.
+    def rolling(self, window, min_periods=None):
+        return Rolling(self, window=window, min_periods=min_periods)
 
     # TODO: 'center' and 'axis' parameter should be implemented.
     #   'axis' implementation, refer https://github.com/databricks/koalas/pull/607

databricks/koalas/groupby.py

@@ -1648,8 +1648,8 @@ def nunique(self, dropna=True):
                  F.when(F.count(F.when(col.isNull(), 1).otherwise(None)) >= 1, 1).otherwise(0))
         return self._reduce_for_stat_function(stat_function, only_numeric=False)
 
-    def rolling(self, *args, **kwargs):
-        return RollingGroupby(self)
+    def rolling(self, window, *args, **kwargs):
+        return RollingGroupby(self, window)
 
     def expanding(self, *args, **kwargs):
         return ExpandingGroupby(self)

databricks/koalas/missing/window.py

@@ -71,14 +71,10 @@ class _MissingPandasLikeRolling(object):
     count = unsupported_function_rolling("count")
     cov = unsupported_function_rolling("cov")
     kurt = unsupported_function_rolling("kurt")
-    max = unsupported_function_rolling("max")
-    mean = unsupported_function_rolling("mean")
     median = unsupported_function_rolling("median")
-    min = unsupported_function_rolling("min")
     quantile = unsupported_function_rolling("quantile")
     skew = unsupported_function_rolling("skew")
     std = unsupported_function_rolling("std")
-    sum = unsupported_function_rolling("sum")
     validate = unsupported_function_rolling("validate")
     var = unsupported_function_rolling("var")
 
@@ -120,14 +116,10 @@ class _MissingPandasLikeRollingGroupby(object):
     count = unsupported_function_rolling("count")
     cov = unsupported_function_rolling("cov")
     kurt = unsupported_function_rolling("kurt")
-    max = unsupported_function_rolling("max")
-    mean = unsupported_function_rolling("mean")
     median = unsupported_function_rolling("median")
-    min = unsupported_function_rolling("min")
     quantile = unsupported_function_rolling("quantile")
     skew = unsupported_function_rolling("skew")
     std = unsupported_function_rolling("std")
-    sum = unsupported_function_rolling("sum")
     validate = unsupported_function_rolling("validate")
     var = unsupported_function_rolling("var")
 

databricks/koalas/tests/test_rolling.py

@@ -0,0 +1,55 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You 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 databricks.koalas as ks
+from databricks.koalas.testing.utils import ReusedSQLTestCase, TestUtils
+from databricks.koalas.window import Rolling
+
+
+class RollingTests(ReusedSQLTestCase, TestUtils):
+
+    def test_rolling_error(self):
+        with self.assertRaisesRegex(ValueError, "window must be >= 0"):
+            ks.range(10).rolling(window=-1)
+        with self.assertRaisesRegex(ValueError, "min_periods must be >= 0"):
+            ks.range(10).rolling(window=1, min_periods=-1)
+
+        with self.assertRaisesRegex(
+                TypeError,
+                "kdf_or_kser must be a series or dataframe; however, got:.*int"):
+            Rolling(1, 2)
+
+    def _test_rolling_func(self, f):
+        kser = ks.Series([1, 2, 3])
+        pser = kser.to_pandas()
+        self.assert_eq(repr(getattr(kser.rolling(2), f)()), repr(getattr(pser.rolling(2), f)()))
+
+        kdf = ks.DataFrame({'a': [1, 2, 3, 2], 'b': [4.0, 2.0, 3.0, 1.0]})
+        pdf = kdf.to_pandas()
+        self.assert_eq(repr(getattr(kdf.rolling(2), f)()), repr(getattr(pdf.rolling(2), f)()))
+
+    def test_rolling_min(self):
+        self._test_rolling_func("min")
+
+    def test_rolling_max(self):
+        self._test_rolling_func("max")
+
+    def test_rolling_mean(self):
+        self._test_rolling_func("mean")
+
+    def test_rolling_sum(self):
+        self._test_rolling_func("sum")