Add std and var at rolling and expanding in Series, Frame, SeriesGrou…

…pBy, FrameGroupBy

databricks/koalas/missing/window.py

@@ -49,9 +49,7 @@ class _MissingPandasLikeExpanding(object):
     median = unsupported_function_expanding("median")
     quantile = unsupported_function_expanding("quantile")
     skew = unsupported_function_expanding("skew")
-    std = unsupported_function_expanding("std")
     validate = unsupported_function_expanding("validate")
-    var = unsupported_function_expanding("var")
 
     exclusions = unsupported_property_expanding("exclusions")
     is_datetimelike = unsupported_property_expanding("is_datetimelike")
@@ -69,9 +67,7 @@ class _MissingPandasLikeRolling(object):
     median = unsupported_function_rolling("median")
     quantile = unsupported_function_rolling("quantile")
     skew = unsupported_function_rolling("skew")
-    std = unsupported_function_rolling("std")
     validate = unsupported_function_rolling("validate")
-    var = unsupported_function_rolling("var")
 
     exclusions = unsupported_property_rolling("exclusions")
     is_datetimelike = unsupported_property_rolling("is_datetimelike")
@@ -89,9 +85,7 @@ class _MissingPandasLikeExpandingGroupby(object):
     median = unsupported_function_expanding("median")
     quantile = unsupported_function_expanding("quantile")
     skew = unsupported_function_expanding("skew")
-    std = unsupported_function_expanding("std")
     validate = unsupported_function_expanding("validate")
-    var = unsupported_function_expanding("var")
 
     exclusions = unsupported_property_expanding("exclusions")
     is_datetimelike = unsupported_property_expanding("is_datetimelike")
@@ -109,9 +103,7 @@ class _MissingPandasLikeRollingGroupby(object):
     median = unsupported_function_rolling("median")
     quantile = unsupported_function_rolling("quantile")
     skew = unsupported_function_rolling("skew")
-    std = unsupported_function_rolling("std")
     validate = unsupported_function_rolling("validate")
-    var = unsupported_function_rolling("var")
 
     exclusions = unsupported_property_rolling("exclusions")
     is_datetimelike = unsupported_property_rolling("is_datetimelike")

databricks/koalas/tests/test_expanding.py

@@ -72,6 +72,12 @@ def test_expanding_mean(self):
     def test_expanding_sum(self):
         self._test_expanding_func("sum")
 
+    def test_expanding_std(self):
+        self._test_expanding_func("std")
+
+    def test_expanding_var(self):
+        self._test_expanding_func("var")
+
     def _test_groupby_expanding_func(self, f):
         kser = ks.Series([1, 2, 3])
         pser = kser.to_pandas()
@@ -117,3 +123,9 @@ def test_groupby_expanding_mean(self):
 
     def test_groupby_expanding_sum(self):
         self._test_groupby_expanding_func("sum")
+
+    def test_groupby_expanding_std(self):
+        self._test_groupby_expanding_func("std")
+
+    def test_groupby_expanding_var(self):
+        self._test_groupby_expanding_func("var")

databricks/koalas/tests/test_rolling.py

@@ -75,6 +75,12 @@ def test_rolling_sum(self):
     def test_rolling_count(self):
         self._test_rolling_func("count")
 
+    def test_rolling_std(self):
+        self._test_rolling_func("std")
+
+    def test_rolling_var(self):
+        self._test_rolling_func("var")
+
     def _test_groupby_rolling_func(self, f):
         kser = ks.Series([1, 2, 3])
         pser = kser.to_pandas()
@@ -111,3 +117,9 @@ def test_groupby_rolling_mean(self):
 
     def test_groupby_rolling_sum(self):
         self._test_groupby_rolling_func("sum")
+
+    def test_groupby_rolling_std(self):
+        self._test_groupby_rolling_func("std")
+
+    def test_groupby_rolling_var(self):
+        self._test_groupby_rolling_func("var")