Feature/support bn 1 1 (#1278)

* add rolling.var and allow min_periods for bottleck version 1.1 and later

* add TODO note for updating minimum suported bottleneck version

Author: Joe Hamman

doc/whats-new.rst

@@ -21,6 +21,10 @@ v0.9.2 (unreleased)
 
 Enhancements
 ~~~~~~~~~~~~
+- When bottleneck version 1.1 or later is installed, use bottleneck for rolling
+  `var`, `argmin`, `argmax`, and `rank` computations. Also, `rolling.median`
+  now also accepts a `min_periods` argument (:issue:`1276`).
+  By `Joe Hamman <https://github.com/jhamman>`_.
 
 Bug fixes
 ~~~~~~~~~

xarray/core/ops.py

@@ -52,7 +52,8 @@
 NAN_CUM_METHODS = ['cumsum', 'cumprod']
 BOTTLENECK_ROLLING_METHODS = {'move_sum': 'sum', 'move_mean': 'mean',
                               'move_std': 'std', 'move_min': 'min',
-                              'move_max': 'max'}
+                              'move_max': 'max', 'move_var': 'var',
+                              'move_argmin': 'argmin', 'move_argmax': 'argmax'}
 # TODO: wrap take, dot, sort
 
 
@@ -520,24 +521,42 @@ def inject_bottleneck_rolling_methods(cls):
     for name, f in methods:
         func = cls._reduce_method(f)
         func.__name__ = name
-        func.__doc__ = _ROLLING_REDUCE_DOCSTRING_TEMPLATE.format(name=func.__name__)
+        func.__doc__ = _ROLLING_REDUCE_DOCSTRING_TEMPLATE.format(
+            name=func.__name__)
         setattr(cls, name, func)
 
     # bottleneck rolling methods
     if has_bottleneck:
-        if LooseVersion(bn.__version__) < LooseVersion('1.0'):
+        # TODO: Bump the required version of bottlneck to 1.1 and remove all
+        # these version checks (see GH#1278)
+        bn_version = LooseVersion(bn.__version__)
+        bn_min_version = LooseVersion('1.0')
+        bn_version_1_1 = LooseVersion('1.1')
+        if bn_version < bn_min_version:
             return
 
         for bn_name, method_name in BOTTLENECK_ROLLING_METHODS.items():
-            f = getattr(bn, bn_name)
-            func = cls._bottleneck_reduce(f)
-            func.__name__ = method_name
-            func.__doc__ = _ROLLING_REDUCE_DOCSTRING_TEMPLATE.format(name=func.__name__)
-            setattr(cls, method_name, func)
-
-        # bottleneck rolling methods without min_count
+            try:
+                f = getattr(bn, bn_name)
+                func = cls._bottleneck_reduce(f)
+                func.__name__ = method_name
+                func.__doc__ = _ROLLING_REDUCE_DOCSTRING_TEMPLATE.format(
+                    name=func.__name__)
+                setattr(cls, method_name, func)
+            except AttributeError as e:
+                # skip functions not in Bottleneck 1.0
+                if ((bn_version < bn_version_1_1) and
+                        (bn_name not in ['move_var', 'move_argmin',
+                                         'move_argmax', 'move_rank'])):
+                    raise e
+
+        # bottleneck rolling methods without min_count (bn.__version__ < 1.1)
         f = getattr(bn, 'move_median')
-        func = cls._bottleneck_reduce_without_min_count(f)
+        if bn_version >= bn_version_1_1:
+            func = cls._bottleneck_reduce(f)
+        else:
+            func = cls._bottleneck_reduce_without_min_count(f)
         func.__name__ = 'median'
-        func.__doc__ = _ROLLING_REDUCE_DOCSTRING_TEMPLATE.format(name=func.__name__)
+        func.__doc__ = _ROLLING_REDUCE_DOCSTRING_TEMPLATE.format(
+            name=func.__name__)
         setattr(cls, 'median', func)

xarray/tests/test_dataarray.py

@@ -2448,16 +2448,24 @@ def test_rolling_properties(da):
     assert 'min_periods must be greater than zero' in str(exception)
 
 
-@pytest.mark.parametrize('name', ('sum', 'mean', 'std', 'min', 'max', 'median'))
+@pytest.mark.parametrize('name', ('sum', 'mean', 'std', 'var',
+                                  'min', 'max', 'median'))
 @pytest.mark.parametrize('center', (True, False, None))
 @pytest.mark.parametrize('min_periods', (1, None))
 def test_rolling_wrapped_bottleneck(da, name, center, min_periods):
     pytest.importorskip('bottleneck')
     import bottleneck as bn
 
-    # skip if median and min_periods
-    if (min_periods == 1) and (name == 'median'):
-        pytest.skip()
+    # skip if median and min_periods bottleneck version < 1.1
+    if ((min_periods == 1) and
+        (name == 'median') and
+            (LooseVersion(bn.__version__) < LooseVersion('1.1'))):
+        pytest.skip('rolling median accepts min_periods for bottleneck 1.1')
+
+    # skip if var and bottleneck version < 1.1
+    if ((name == 'median') and
+            (LooseVersion(bn.__version__) < LooseVersion('1.1'))):
+        pytest.skip('rolling median accepts min_periods for bottleneck 1.1')
 
     # Test all bottleneck functions
     rolling_obj = da.rolling(time=7, min_periods=min_periods)
@@ -2473,8 +2481,12 @@ def test_rolling_wrapped_bottleneck(da, name, center, min_periods):
     actual = getattr(rolling_obj, name)()['time']
     assert_equal(actual, da['time'])
 
+
 def test_rolling_invalid_args(da):
-    pytest.importorskip('bottleneck')
+    pytest.importorskip('bottleneck', minversion="1.0")
+    import bottleneck as bn
+    if LooseVersion(bn.__version__) >= LooseVersion('1.1'):
+        pytest.skip('rolling median accepts min_periods for bottleneck 1.1')
     with pytest.raises(ValueError) as exception:
         da.rolling(time=7, min_periods=1).median()
     assert 'Rolling.median does not' in str(exception)