From 40df7b0b73d97c053b4e8c7194b9bf2419a66f08 Mon Sep 17 00:00:00 2001
From: Yves Delley <hack@delley.net>
Date: Tue, 20 Sep 2016 16:49:56 +0200
Subject: [PATCH 1/8] use asanyarray instead of asarray in data accessor of
 Variable.

---
 xarray/core/variable.py        |  2 +-
 xarray/test/test_quantities.py | 55 ++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+), 1 deletion(-)
 create mode 100644 xarray/test/test_quantities.py

diff --git a/xarray/core/variable.py b/xarray/core/variable.py
index 6aafbcaab82..66985f91896 100644
--- a/xarray/core/variable.py
+++ b/xarray/core/variable.py
@@ -185,7 +185,7 @@ def _as_array_or_item(data):
 
     TODO: remove this (replace with np.asarray) once these issues are fixed
     """
-    data = np.asarray(data)
+    data = np.asanyarray(data)
     if data.ndim == 0:
         if data.dtype.kind == 'M':
             data = np.datetime64(data, 'ns')
diff --git a/xarray/test/test_quantities.py b/xarray/test/test_quantities.py
new file mode 100644
index 00000000000..7d8f61b562e
--- /dev/null
+++ b/xarray/test/test_quantities.py
@@ -0,0 +1,55 @@
+import numpy as np
+import pandas as pd
+
+from xarray import (align, broadcast, Dataset, DataArray, Variable)
+
+from xarray.test import (TestCase, unittest)
+
+try:
+    import quantities as pq
+    has_quantities = True
+except ImportError:
+    has_quantities = False
+
+def requires_quantities(test):
+    return test if has_quantities else unittest.skip('requires dask')(test)
+
+@requires_quantities
+class TestWithQuantities(TestCase):
+    def setUp(self):
+        self.x = np.arange(10) * pq.A
+        self.y = np.arange(20)
+        self.xp = np.arange(10) * pq.J
+        self.v = np.arange(10*20).reshape(10,20) * pq.V
+        self.da = DataArray(self.v,dims=['x','y'],coords=dict(x=self.x,y=self.y,xp=(['x'],self.xp)))
+
+    def assertEqualWUnits(self,a,b):
+        self.assertIsNotNone(getattr(a, 'units', None))
+        self.assertIsNotNone(getattr(b, 'units', None))
+        self.assertEqual(a.units,b.units)
+        np.testing.assert_allclose(a.magnitude,b.magnitude)
+
+    def test_units_in_data_and_coords(self):
+        da = self.da
+        self.assertEqualWUnits(da.xp.data,self.xp)
+        self.assertEqualWUnits(da.data,self.v)
+
+    def test_arithmetics(self):
+        da = self.da
+        f = DataArray(np.arange(10*20).reshape(10,20)*pq.A,dims=['x','y'],coords=dict(x=self.x,y=self.y))
+        self.assertEqualWUnits((da*f).data, da.data*f.data)
+
+    def test_unit_checking(self):
+        da = self.da
+        f = DataArray(np.arange(10*20).reshape(10,20)*pq.A,dims=['x','y'],coords=dict(x=self.x,y=self.y))
+        with self.assertRaisesRegex(ValueError,'Unable to convert between units'):
+            da + f
+
+    @unittest.expectedFailure
+    def test_units_in_indexes(self):
+        """
+        Indexes are borrowed from Pandas, and Pandas does not support units.
+        Therefore, we currently don't intend to support units on idexes either.
+        """
+        da = self.da
+        self.assertEqualWUnits(da.x.data,self.x)
\ No newline at end of file

From 37b484c8e0336c6ddb2c2c332b2b7c2a557272fd Mon Sep 17 00:00:00 2001
From: Yves Delley <hack@delley.net>
Date: Wed, 5 Oct 2016 19:51:15 +0200
Subject: [PATCH 2/8] added tests for a few operations

---
 xarray/test/test_quantities.py | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/xarray/test/test_quantities.py b/xarray/test/test_quantities.py
index 7d8f61b562e..58281731b59 100644
--- a/xarray/test/test_quantities.py
+++ b/xarray/test/test_quantities.py
@@ -52,4 +52,11 @@ def test_units_in_indexes(self):
         Therefore, we currently don't intend to support units on idexes either.
         """
         da = self.da
-        self.assertEqualWUnits(da.x.data,self.x)
\ No newline at end of file
+        self.assertEqualWUnits(da.x.data,self.x)
+
+    def test_sel(self):
+        self.assertEqualWUnits(self.da.sel(y=self.y[0]).values,self.v[:,0])
+
+    def test_mean(self):
+        self.assertEqualWUnits(self.da.mean('x').values,self.v.mean(0))
+

From 921915ed45d40d9b8a694fb5d8a7e2d8efe34693 Mon Sep 17 00:00:00 2001
From: Yves Delley <hack@delley.net>
Date: Mon, 14 Nov 2016 11:49:50 +0100
Subject: [PATCH 3/8] small typo

---
 xarray/test/test_quantities.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xarray/test/test_quantities.py b/xarray/test/test_quantities.py
index 58281731b59..a0d4e20f44d 100644
--- a/xarray/test/test_quantities.py
+++ b/xarray/test/test_quantities.py
@@ -49,7 +49,7 @@ def test_unit_checking(self):
     def test_units_in_indexes(self):
         """
         Indexes are borrowed from Pandas, and Pandas does not support units.
-        Therefore, we currently don't intend to support units on idexes either.
+        Therefore, we currently don't intend to support units on indexes either.
         """
         da = self.da
         self.assertEqualWUnits(da.x.data,self.x)

From b3a49b6410895051c5a8a7fa37d7a2e0e9ffa743 Mon Sep 17 00:00:00 2001
From: Yves Delley <hack@delley.net>
Date: Mon, 14 Nov 2016 12:57:47 +0100
Subject: [PATCH 4/8] marked failing tests as expected

---
 xarray/test/test_quantities.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/xarray/test/test_quantities.py b/xarray/test/test_quantities.py
index a0d4e20f44d..916e801241d 100644
--- a/xarray/test/test_quantities.py
+++ b/xarray/test/test_quantities.py
@@ -54,9 +54,11 @@ def test_units_in_indexes(self):
         da = self.da
         self.assertEqualWUnits(da.x.data,self.x)
 
+    @unittest.expectedFailure
     def test_sel(self):
         self.assertEqualWUnits(self.da.sel(y=self.y[0]).values,self.v[:,0])
 
+    @unittest.expectedFailure
     def test_mean(self):
         self.assertEqualWUnits(self.da.mean('x').values,self.v.mean(0))
 

From 28ef3996acf402cb9918f0b4e982f146a85d39f6 Mon Sep 17 00:00:00 2001
From: Yves Delley <hack@delley.net>
Date: Wed, 16 Nov 2016 11:28:12 +0100
Subject: [PATCH 5/8] fixed dependency message for quantities testing, and
 added quantities to CI requirements

---
 ci/requirements-py27-cdat+pynio.yml  | 1 +
 ci/requirements-py27-netcdf4-dev.yml | 1 +
 ci/requirements-py27-pydap.yml       | 1 +
 ci/requirements-py33.yml             | 1 +
 ci/requirements-py34.yml             | 1 +
 ci/requirements-py35-dask-dev.yml    | 1 +
 ci/requirements-py35-pandas-dev.yml  | 1 +
 ci/requirements-py35.yml             | 1 +
 xarray/test/test_quantities.py       | 2 +-
 9 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/ci/requirements-py27-cdat+pynio.yml b/ci/requirements-py27-cdat+pynio.yml
index 53aafb058e1..abfb55fc593 100644
--- a/ci/requirements-py27-cdat+pynio.yml
+++ b/ci/requirements-py27-cdat+pynio.yml
@@ -14,3 +14,4 @@ dependencies:
   - cyordereddict
   - pip:
     - coveralls
+    - quantities
diff --git a/ci/requirements-py27-netcdf4-dev.yml b/ci/requirements-py27-netcdf4-dev.yml
index a64782de235..14fe2bd3209 100644
--- a/ci/requirements-py27-netcdf4-dev.yml
+++ b/ci/requirements-py27-netcdf4-dev.yml
@@ -12,4 +12,5 @@ dependencies:
     - coveralls
     - pytest-cov
     - h5netcdf
+    - quantities
     - git+https://github.com/Unidata/netcdf4-python.git
diff --git a/ci/requirements-py27-pydap.yml b/ci/requirements-py27-pydap.yml
index 459f049c76a..160581acdc3 100644
--- a/ci/requirements-py27-pydap.yml
+++ b/ci/requirements-py27-pydap.yml
@@ -12,3 +12,4 @@ dependencies:
     - coveralls
     - pytest-cov
     - pydap
+    - quantities
diff --git a/ci/requirements-py33.yml b/ci/requirements-py33.yml
index 7ff08a5794f..98b089e6df5 100644
--- a/ci/requirements-py33.yml
+++ b/ci/requirements-py33.yml
@@ -6,3 +6,4 @@ dependencies:
   - pip:
     - coveralls
     - pytest-cov
+    - quantities
diff --git a/ci/requirements-py34.yml b/ci/requirements-py34.yml
index a49611751ca..e2ab1d0cc3c 100644
--- a/ci/requirements-py34.yml
+++ b/ci/requirements-py34.yml
@@ -7,3 +7,4 @@ dependencies:
   - pip:
     - coveralls
     - pytest-cov
+    - quantities
diff --git a/ci/requirements-py35-dask-dev.yml b/ci/requirements-py35-dask-dev.yml
index eab9ad21877..ed935294401 100644
--- a/ci/requirements-py35-dask-dev.yml
+++ b/ci/requirements-py35-dask-dev.yml
@@ -10,4 +10,5 @@ dependencies:
   - pip:
     - coveralls
     - pytest-cov
+    - quantities
     - git+https://github.com/blaze/dask.git
diff --git a/ci/requirements-py35-pandas-dev.yml b/ci/requirements-py35-pandas-dev.yml
index 74f8abe84f0..4a7f4979f52 100644
--- a/ci/requirements-py35-pandas-dev.yml
+++ b/ci/requirements-py35-pandas-dev.yml
@@ -11,4 +11,5 @@ dependencies:
     - coveralls
     - pytest-cov
     - dask
+    - quantities
     - git+https://github.com/pydata/pandas.git
diff --git a/ci/requirements-py35.yml b/ci/requirements-py35.yml
index 0f3b005ea6a..8c76279c060 100644
--- a/ci/requirements-py35.yml
+++ b/ci/requirements-py35.yml
@@ -15,3 +15,4 @@ dependencies:
     - coveralls
     - pytest-cov
     - h5netcdf
+    - quantities
diff --git a/xarray/test/test_quantities.py b/xarray/test/test_quantities.py
index 916e801241d..96c0101bc2e 100644
--- a/xarray/test/test_quantities.py
+++ b/xarray/test/test_quantities.py
@@ -12,7 +12,7 @@
     has_quantities = False
 
 def requires_quantities(test):
-    return test if has_quantities else unittest.skip('requires dask')(test)
+    return test if has_quantities else unittest.skip('requires python-quantities')(test)
 
 @requires_quantities
 class TestWithQuantities(TestCase):

From c849b677bffb4faed6f30c73a1a0d51b141462c2 Mon Sep 17 00:00:00 2001
From: Yves Delley <hack@delley.net>
Date: Wed, 16 Nov 2016 11:45:49 +0100
Subject: [PATCH 6/8] fixing python 2.7 unittests compatibility issue

---
 xarray/test/test_quantities.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xarray/test/test_quantities.py b/xarray/test/test_quantities.py
index 96c0101bc2e..adce6a3040d 100644
--- a/xarray/test/test_quantities.py
+++ b/xarray/test/test_quantities.py
@@ -42,7 +42,7 @@ def test_arithmetics(self):
     def test_unit_checking(self):
         da = self.da
         f = DataArray(np.arange(10*20).reshape(10,20)*pq.A,dims=['x','y'],coords=dict(x=self.x,y=self.y))
-        with self.assertRaisesRegex(ValueError,'Unable to convert between units'):
+        with self.assertRaisesRegexp(ValueError,'Unable to convert between units'):
             da + f
 
     @unittest.expectedFailure

From 39dedb149086619331ee9f967878b06ce4e3c21a Mon Sep 17 00:00:00 2001
From: Yves Delley <hack@delley.net>
Date: Fri, 18 Nov 2016 14:59:58 +0100
Subject: [PATCH 7/8] implemented some of the improvements suggested by shoyer
 in the unittests

---
 xarray/test/test_quantities.py | 78 ++++++++++++++++++++++++++--------
 1 file changed, 60 insertions(+), 18 deletions(-)

diff --git a/xarray/test/test_quantities.py b/xarray/test/test_quantities.py
index adce6a3040d..1769a81fc57 100644
--- a/xarray/test/test_quantities.py
+++ b/xarray/test/test_quantities.py
@@ -1,3 +1,14 @@
+""" test_quantities: Test storing and using instances of
+:py:class:`quantities.Quantity` inside :py:class`xarray.DataArray`.
+
+It can be considered a stand-in for other :py:class:`numpy.ndarray`
+subclasses, particularly other units implementations such as
+astropy's. As preservation of subclasses is not a guaranteed feature of
+`xarray`, some operations will discard subclasses. This test
+also serves as documnetation which operations do preserve subclasses
+and which don't.
+"""
+
 import numpy as np
 import pandas as pd
 
@@ -7,12 +18,18 @@
 
 try:
     import quantities as pq
+
     has_quantities = True
 except ImportError:
     has_quantities = False
 
+
 def requires_quantities(test):
-    return test if has_quantities else unittest.skip('requires python-quantities')(test)
+    return (
+        test if has_quantities else
+        unittest.skip('requires python-quantities')(test)
+    )
+
 
 @requires_quantities
 class TestWithQuantities(TestCase):
@@ -20,45 +37,70 @@ def setUp(self):
         self.x = np.arange(10) * pq.A
         self.y = np.arange(20)
         self.xp = np.arange(10) * pq.J
-        self.v = np.arange(10*20).reshape(10,20) * pq.V
-        self.da = DataArray(self.v,dims=['x','y'],coords=dict(x=self.x,y=self.y,xp=(['x'],self.xp)))
+        self.v = np.arange(10 * 20).reshape(10, 20) * pq.V
+        self.da = DataArray(self.v, dims=['x', 'y'],
+                            coords=dict(x=self.x, y=self.y, xp=(['x'], self.xp)))
 
-    def assertEqualWUnits(self,a,b):
+    def assertEqualWUnits(self, a, b):
+        # DataArray's are supposed to preserve Quantity instances
+        # but they (currently?) do not expose their behaviour.
+        # We thus need to extract the contained subarray via .data
+        if isinstance(a, DataArray):
+            a = a.data
+        if isinstance(b, DataArray):
+            b = b.data
         self.assertIsNotNone(getattr(a, 'units', None))
         self.assertIsNotNone(getattr(b, 'units', None))
-        self.assertEqual(a.units,b.units)
-        np.testing.assert_allclose(a.magnitude,b.magnitude)
+        self.assertEqual(a.units, b.units)
+        np.testing.assert_allclose(a.magnitude, b.magnitude)
 
     def test_units_in_data_and_coords(self):
         da = self.da
-        self.assertEqualWUnits(da.xp.data,self.xp)
-        self.assertEqualWUnits(da.data,self.v)
+        self.assertEqualWUnits(da.xp.data, self.xp)
+        self.assertEqualWUnits(da.data, self.v)
 
     def test_arithmetics(self):
+        x = self.x
+        y = self.y
+        v = self.v
         da = self.da
-        f = DataArray(np.arange(10*20).reshape(10,20)*pq.A,dims=['x','y'],coords=dict(x=self.x,y=self.y))
-        self.assertEqualWUnits((da*f).data, da.data*f.data)
+
+        f = np.arange(10 * 20).reshape(10, 20) * pq.A
+        g = DataArray(f, dims=['x', 'y'], coords=dict(x=x, y=y))
+        self.assertEqualWUnits(da * g, v * f)
+
+        # swapped dimension order
+        f = np.arange(20 * 10).reshape(20, 10) * pq.V
+        g = DataArray(f, dims=['y', 'x'], coords=dict(x=x, y=y))
+        self.assertEqualWUnits(da + g, v + f.T)
+
+        # broadcasting
+        f = np.arange(10) * pq.m
+        g = DataArray(f, dims=['x'], coords=dict(x=x))
+        self.assertEqualWUnits(da / g, v / f[:,None])
 
     def test_unit_checking(self):
         da = self.da
-        f = DataArray(np.arange(10*20).reshape(10,20)*pq.A,dims=['x','y'],coords=dict(x=self.x,y=self.y))
-        with self.assertRaisesRegexp(ValueError,'Unable to convert between units'):
-            da + f
+        f = np.arange(10 * 20).reshape(10, 20) * pq.A
+        g = DataArray(f, dims=['x', 'y'], coords=dict(x=self.x, y=self.y))
+        with self.assertRaisesRegexp(ValueError,
+                                     'Unable to convert between units'):
+            da + g
 
     @unittest.expectedFailure
     def test_units_in_indexes(self):
-        """
+        """ Test if units survive through xarray indexes.
+
         Indexes are borrowed from Pandas, and Pandas does not support units.
         Therefore, we currently don't intend to support units on indexes either.
         """
         da = self.da
-        self.assertEqualWUnits(da.x.data,self.x)
+        self.assertEqualWUnits(da.x, self.x)
 
     @unittest.expectedFailure
     def test_sel(self):
-        self.assertEqualWUnits(self.da.sel(y=self.y[0]).values,self.v[:,0])
+        self.assertEqualWUnits(self.da.sel(y=self.y[0]), self.v[:, 0])
 
     @unittest.expectedFailure
     def test_mean(self):
-        self.assertEqualWUnits(self.da.mean('x').values,self.v.mean(0))
-
+        self.assertEqualWUnits(self.da.mean('x'), self.v.mean(0))

From c58f92ebccf76253d2eed6b9ec48b835a389209f Mon Sep 17 00:00:00 2001
From: Yves Delley <hack@delley.net>
Date: Fri, 18 Nov 2016 15:41:33 +0100
Subject: [PATCH 8/8] changed preserving ndarray subclasses only for .data but
 not for .values

---
 xarray/core/variable.py | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/xarray/core/variable.py b/xarray/core/variable.py
index 66985f91896..51eb5cf67c5 100644
--- a/xarray/core/variable.py
+++ b/xarray/core/variable.py
@@ -185,7 +185,7 @@ def _as_array_or_item(data):
 
     TODO: remove this (replace with np.asarray) once these issues are fixed
     """
-    data = np.asanyarray(data)
+    data = np.asarray(data)
     if data.ndim == 0:
         if data.dtype.kind == 'M':
             data = np.datetime64(data, 'ns')
@@ -193,6 +193,19 @@ def _as_array_or_item(data):
             data = np.timedelta64(data, 'ns')
     return data
 
+def _as_any_array_or_item(data):
+    """Return the given values as a numpy array subclass instance, or as an
+    individual item if it's a 0d datetime64 or timedelta64 array.
+
+    The same caveats as for :py:meth:`_as_array_or_item` apply.
+    """
+    data = np.asanyarray(data)
+    if data.ndim == 0:
+        if data.dtype.kind == 'M':
+            data = np.datetime64(data, 'ns')
+        elif data.dtype.kind == 'm':
+            data = np.timedelta64(data, 'ns')
+    return data
 
 class Variable(common.AbstractArray, common.SharedMethodsMixin,
                utils.NdimSizeLenMixin):
@@ -267,7 +280,7 @@ def data(self):
         if isinstance(self._data, dask_array_type):
             return self._data
         else:
-            return self.values
+            return _as_any_array_or_item(self._data_cached())
 
     @data.setter
     def data(self, data):