From 95d2008e68565a1a3fc725e212a54d6755fda200 Mon Sep 17 00:00:00 2001
From: discort <odiscort@gmail.com>
Date: Mon, 9 Jan 2017 23:53:17 +0200
Subject: [PATCH 1/6] BUG #14962

---
 pandas/core/resample.py       | 4 ++++
 pandas/tests/test_resample.py | 8 ++++++++
 2 files changed, 12 insertions(+)

diff --git a/pandas/core/resample.py b/pandas/core/resample.py
index 2bb825541e23b..d794e033fd60e 100644
--- a/pandas/core/resample.py
+++ b/pandas/core/resample.py
@@ -697,6 +697,10 @@ def _downsample(self, how, **kwargs):
         if not len(ax):
             # reset to the new freq
             obj = obj.copy()
+            if how == "size" and isinstance(obj, pd.DataFrame):
+                obj = obj.groupby(
+                    self.grouper, axis=self.axis).aggregate(how, **kwargs)
+
             obj.index.freq = self.freq
             return obj
 
diff --git a/pandas/tests/test_resample.py b/pandas/tests/test_resample.py
index 959e3d2f459ce..4a35af262a76c 100644
--- a/pandas/tests/test_resample.py
+++ b/pandas/tests/test_resample.py
@@ -848,6 +848,14 @@ def test_resample_loffset_arg_type(self):
                 assert_frame_equal(result_agg, expected)
                 assert_frame_equal(result_how, expected)
 
+    def test_resample_empty_dataframe_with_size(self):
+        # GH 14962
+        df1 = pd.DataFrame(dict(a=range(100)),
+                           index=pd.date_range('1/1/2000', periods=100, freq="M"))
+        df2 = df1[df1.a < 0]
+        result = df2.resample("Q").size()
+        assertIsInstance(result, pd.Series)
+
 
 class TestDatetimeIndex(Base):
     _index_factory = lambda x: date_range

From 8f7b43734e15839349fd4412e4bcb5e1458bb9a3 Mon Sep 17 00:00:00 2001
From: discort <odiscort@gmail.com>
Date: Thu, 12 Jan 2017 00:18:26 +0200
Subject: [PATCH 2/6] BUG: added series type to wrap_result for empty DataFrame

---
 doc/source/whatsnew/v0.19.0.txt |  1 +
 pandas/core/resample.py         | 15 ++++++++++-----
 pandas/tests/test_resample.py   | 30 +++++++++++++++++++++---------
 3 files changed, 32 insertions(+), 14 deletions(-)

diff --git a/doc/source/whatsnew/v0.19.0.txt b/doc/source/whatsnew/v0.19.0.txt
index bc5e278df743f..00467e3608d54 100644
--- a/doc/source/whatsnew/v0.19.0.txt
+++ b/doc/source/whatsnew/v0.19.0.txt
@@ -1563,3 +1563,4 @@ Bug Fixes
 - ``PeriodIndex`` can now accept ``list`` and ``array`` which contains ``pd.NaT`` (:issue:`13430`)
 - Bug in ``df.groupby`` where ``.median()`` returns arbitrary values if grouped dataframe contains empty bins (:issue:`13629`)
 - Bug in ``Index.copy()`` where ``name`` parameter was ignored (:issue:`14302`)
+- Bug in ``_downsample()``. Inconsistent return type on resample of empty DataFrame (:issue:`14962`)
\ No newline at end of file
diff --git a/pandas/core/resample.py b/pandas/core/resample.py
index d794e033fd60e..df888a97e4949 100644
--- a/pandas/core/resample.py
+++ b/pandas/core/resample.py
@@ -697,12 +697,8 @@ def _downsample(self, how, **kwargs):
         if not len(ax):
             # reset to the new freq
             obj = obj.copy()
-            if how == "size" and isinstance(obj, pd.DataFrame):
-                obj = obj.groupby(
-                    self.grouper, axis=self.axis).aggregate(how, **kwargs)
-
             obj.index.freq = self.freq
-            return obj
+            return self._wrap_result(obj)
 
         # do we have a regular frequency
         if ax.freq is not None or ax.inferred_freq is not None:
@@ -773,6 +769,15 @@ def _wrap_result(self, result):
         # convert if needed
         if self.kind == 'period' and not isinstance(result.index, PeriodIndex):
             result.index = result.index.to_period(self.freq)
+
+        # Make consistent type of result. GH14962
+        if not len(self.ax):
+            grouper = BinGrouper([], result.index)
+            grouped = self._selected_obj.groupby(grouper)
+            result = pd.Series([],
+                               index=result.index,
+                               name=grouped.name,
+                               dtype='int64')
         return result
 
 
diff --git a/pandas/tests/test_resample.py b/pandas/tests/test_resample.py
index 4a35af262a76c..afcef2160f4dd 100644
--- a/pandas/tests/test_resample.py
+++ b/pandas/tests/test_resample.py
@@ -773,8 +773,18 @@ def test_resample_empty_series(self):
                 expected = s.copy()
                 expected.index = s.index._shallow_copy(freq=freq)
                 assert_index_equal(result.index, expected.index)
-                assert result.index.freq == expected.index.freq
-                assert_series_equal(result, expected, check_dtype=False)
+
+                self.assertEqual(result.index.freq, expected.index.freq)
+
+                if (method == 'size' and
+                    isinstance(result.index, PeriodIndex) and
+                        freq in ['M', 'D']):
+                    # GH12871 - TODO: name should propagate, but currently
+                    # doesn't on lower / same frequency with PeriodIndex
+                    assert_series_equal(result, expected, check_dtype=False)
+
+                else:
+                    assert_series_equal(result, expected, check_dtype=False)
 
     def test_resample_empty_dataframe(self):
         # GH13212
@@ -783,11 +793,11 @@ def test_resample_empty_dataframe(self):
 
         for freq in ['M', 'D', 'H']:
             # count retains dimensions too
-            methods = downsample_methods + ['count']
+            methods = downsample_methods + upsample_methods
             for method in methods:
                 result = getattr(f.resample(freq), method)()
 
-                expected = f.copy()
+                expected = pd.Series([])
                 expected.index = f.index._shallow_copy(freq=freq)
                 assert_index_equal(result.index, expected.index)
                 assert result.index.freq == expected.index.freq
@@ -850,11 +860,13 @@ def test_resample_loffset_arg_type(self):
 
     def test_resample_empty_dataframe_with_size(self):
         # GH 14962
-        df1 = pd.DataFrame(dict(a=range(100)),
-                           index=pd.date_range('1/1/2000', periods=100, freq="M"))
-        df2 = df1[df1.a < 0]
-        result = df2.resample("Q").size()
-        assertIsInstance(result, pd.Series)
+        index = pd.DatetimeIndex([], freq='M')
+        df = pd.DataFrame([], index=index)
+
+        for freq in ['M', 'D', 'H']:
+            result = df.resample(freq).size()
+            expected = pd.Series([], index=index, dtype='int64')
+            assert_series_equal(result, expected)
 
 
 class TestDatetimeIndex(Base):

From 37ba820ab2b59e258a9412cb7c0cf8d9723bd088 Mon Sep 17 00:00:00 2001
From: discort <odiscort@gmail.com>
Date: Wed, 25 Jan 2017 09:49:41 +0200
Subject: [PATCH 3/6] added explicit 'size' method and defined logic there

---
 doc/source/whatsnew/v0.19.0.txt |  1 -
 doc/source/whatsnew/v0.20.0.txt |  1 +
 pandas/core/resample.py         | 20 +++++++++-----------
 pandas/tests/test_resample.py   | 21 +++++++++------------
 4 files changed, 19 insertions(+), 24 deletions(-)

diff --git a/doc/source/whatsnew/v0.19.0.txt b/doc/source/whatsnew/v0.19.0.txt
index 00467e3608d54..bc5e278df743f 100644
--- a/doc/source/whatsnew/v0.19.0.txt
+++ b/doc/source/whatsnew/v0.19.0.txt
@@ -1563,4 +1563,3 @@ Bug Fixes
 - ``PeriodIndex`` can now accept ``list`` and ``array`` which contains ``pd.NaT`` (:issue:`13430`)
 - Bug in ``df.groupby`` where ``.median()`` returns arbitrary values if grouped dataframe contains empty bins (:issue:`13629`)
 - Bug in ``Index.copy()`` where ``name`` parameter was ignored (:issue:`14302`)
-- Bug in ``_downsample()``. Inconsistent return type on resample of empty DataFrame (:issue:`14962`)
\ No newline at end of file
diff --git a/doc/source/whatsnew/v0.20.0.txt b/doc/source/whatsnew/v0.20.0.txt
index 9d475390175b2..cbb256321fc0a 100644
--- a/doc/source/whatsnew/v0.20.0.txt
+++ b/doc/source/whatsnew/v0.20.0.txt
@@ -1685,6 +1685,7 @@ Groupby/Resample/Rolling
 - Bug in ``.rolling()`` where ``pd.Timedelta`` or ``datetime.timedelta`` was not accepted as a ``window`` argument (:issue:`15440`)
 - Bug in ``Rolling.quantile`` function that caused a segmentation fault when called with a quantile value outside of the range [0, 1] (:issue:`15463`)
 - Bug in ``DataFrame.resample().median()`` if duplicate column names are present (:issue:`14233`)
+- Bug in ``resample().size()``. Inconsistent return type on resample of empty DataFrame (:issue:`14962`)
 
 Sparse
 ^^^^^^
diff --git a/pandas/core/resample.py b/pandas/core/resample.py
index df888a97e4949..eaa798f0ca225 100644
--- a/pandas/core/resample.py
+++ b/pandas/core/resample.py
@@ -17,6 +17,7 @@
 from pandas.core.indexes.period import PeriodIndex, period_range
 import pandas.core.common as com
 import pandas.core.algorithms as algos
+from pandas.types.generic import ABCDataFrame
 
 import pandas.compat as compat
 from pandas.compat.numpy import function as nv
@@ -549,7 +550,13 @@ def var(self, ddof=1, *args, **kwargs):
         nv.validate_resampler_func('var', args, kwargs)
         return self._downsample('var', ddof=ddof)
 
-
+    @Appender(GroupBy.size.__doc__)
+    def size(self):
+        # It 'seems' special and needs extra handling. GH14962
+        result = self._downsample('size')
+        if not len(self.ax) and isinstance(self._selected_obj, ABCDataFrame):
+            result = pd.Series([], index=result.index, dtype='int64')
+        return result
 Resampler._deprecated_valids += dir(Resampler)
 
 # downsample methods
@@ -563,8 +570,7 @@ def f(self, _method=method, *args, **kwargs):
     setattr(Resampler, method, f)
 
 # groupby & aggregate methods
-for method in ['count', 'size']:
-
+for method in ['count']:
     def f(self, _method=method):
         return self._downsample(_method)
     f.__doc__ = getattr(GroupBy, method).__doc__
@@ -770,14 +776,6 @@ def _wrap_result(self, result):
         if self.kind == 'period' and not isinstance(result.index, PeriodIndex):
             result.index = result.index.to_period(self.freq)
 
-        # Make consistent type of result. GH14962
-        if not len(self.ax):
-            grouper = BinGrouper([], result.index)
-            grouped = self._selected_obj.groupby(grouper)
-            result = pd.Series([],
-                               index=result.index,
-                               name=grouped.name,
-                               dtype='int64')
         return result
 
 
diff --git a/pandas/tests/test_resample.py b/pandas/tests/test_resample.py
index afcef2160f4dd..1a019d4c3615a 100644
--- a/pandas/tests/test_resample.py
+++ b/pandas/tests/test_resample.py
@@ -796,8 +796,14 @@ def test_resample_empty_dataframe(self):
             methods = downsample_methods + upsample_methods
             for method in methods:
                 result = getattr(f.resample(freq), method)()
-
-                expected = pd.Series([])
+                if method != 'size':
+                    expected = f.copy()
+                    assert_equal = assert_frame_equal
+                else:
+                    # GH14962
+                    expected = Series([])
+                    assert_equal = assert_series_equal
+                
                 expected.index = f.index._shallow_copy(freq=freq)
                 assert_index_equal(result.index, expected.index)
                 assert result.index.freq == expected.index.freq
@@ -805,6 +811,7 @@ def test_resample_empty_dataframe(self):
 
             # test size for GH13212 (currently stays as df)
 
+
     def test_resample_empty_dtypes(self):
 
         # Empty series were sometimes causing a segfault (for the functions
@@ -858,16 +865,6 @@ def test_resample_loffset_arg_type(self):
                 assert_frame_equal(result_agg, expected)
                 assert_frame_equal(result_how, expected)
 
-    def test_resample_empty_dataframe_with_size(self):
-        # GH 14962
-        index = pd.DatetimeIndex([], freq='M')
-        df = pd.DataFrame([], index=index)
-
-        for freq in ['M', 'D', 'H']:
-            result = df.resample(freq).size()
-            expected = pd.Series([], index=index, dtype='int64')
-            assert_series_equal(result, expected)
-
 
 class TestDatetimeIndex(Base):
     _index_factory = lambda x: date_range

From 43b26139d330157baf296080b9c0f5dea67db4ed Mon Sep 17 00:00:00 2001
From: discort <odiscort@gmail.com>
Date: Wed, 5 Apr 2017 11:35:59 +0300
Subject: [PATCH 4/6] fixed lint warnings

---
 pandas/core/resample.py       | 2 ++
 pandas/tests/test_resample.py | 3 +--
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/pandas/core/resample.py b/pandas/core/resample.py
index eaa798f0ca225..8f137d6038830 100644
--- a/pandas/core/resample.py
+++ b/pandas/core/resample.py
@@ -557,6 +557,8 @@ def size(self):
         if not len(self.ax) and isinstance(self._selected_obj, ABCDataFrame):
             result = pd.Series([], index=result.index, dtype='int64')
         return result
+
+
 Resampler._deprecated_valids += dir(Resampler)
 
 # downsample methods
diff --git a/pandas/tests/test_resample.py b/pandas/tests/test_resample.py
index 1a019d4c3615a..2eee5f4beca45 100644
--- a/pandas/tests/test_resample.py
+++ b/pandas/tests/test_resample.py
@@ -803,7 +803,7 @@ def test_resample_empty_dataframe(self):
                     # GH14962
                     expected = Series([])
                     assert_equal = assert_series_equal
-                
+
                 expected.index = f.index._shallow_copy(freq=freq)
                 assert_index_equal(result.index, expected.index)
                 assert result.index.freq == expected.index.freq
@@ -811,7 +811,6 @@ def test_resample_empty_dataframe(self):
 
             # test size for GH13212 (currently stays as df)
 
-
     def test_resample_empty_dtypes(self):
 
         # Empty series were sometimes causing a segfault (for the functions

From c0e06b8eb3dba26adaec8bc447e0af6f1c4c351a Mon Sep 17 00:00:00 2001
From: discort <odiscort@gmail.com>
Date: Mon, 12 Jun 2017 23:08:19 +0300
Subject: [PATCH 5/6] Updated tests for resampling of empty dataframes

---
 doc/source/whatsnew/v0.20.0.txt |  1 -
 doc/source/whatsnew/v0.21.0.txt |  1 +
 pandas/core/resample.py         |  5 ++---
 pandas/tests/test_resample.py   | 20 +++++---------------
 4 files changed, 8 insertions(+), 19 deletions(-)

diff --git a/doc/source/whatsnew/v0.20.0.txt b/doc/source/whatsnew/v0.20.0.txt
index cbb256321fc0a..9d475390175b2 100644
--- a/doc/source/whatsnew/v0.20.0.txt
+++ b/doc/source/whatsnew/v0.20.0.txt
@@ -1685,7 +1685,6 @@ Groupby/Resample/Rolling
 - Bug in ``.rolling()`` where ``pd.Timedelta`` or ``datetime.timedelta`` was not accepted as a ``window`` argument (:issue:`15440`)
 - Bug in ``Rolling.quantile`` function that caused a segmentation fault when called with a quantile value outside of the range [0, 1] (:issue:`15463`)
 - Bug in ``DataFrame.resample().median()`` if duplicate column names are present (:issue:`14233`)
-- Bug in ``resample().size()``. Inconsistent return type on resample of empty DataFrame (:issue:`14962`)
 
 Sparse
 ^^^^^^
diff --git a/doc/source/whatsnew/v0.21.0.txt b/doc/source/whatsnew/v0.21.0.txt
index 36ca79e8b8714..c9f84b37ad874 100644
--- a/doc/source/whatsnew/v0.21.0.txt
+++ b/doc/source/whatsnew/v0.21.0.txt
@@ -112,6 +112,7 @@ Plotting
 
 Groupby/Resample/Rolling
 ^^^^^^^^^^^^^^^^^^^^^^^^
+- Bug in ``resample().size()``. Inconsistent return type on resample of empty DataFrame (:issue:`14962`)
 
 
 
diff --git a/pandas/core/resample.py b/pandas/core/resample.py
index 8f137d6038830..f5c615f2b4db9 100644
--- a/pandas/core/resample.py
+++ b/pandas/core/resample.py
@@ -17,7 +17,7 @@
 from pandas.core.indexes.period import PeriodIndex, period_range
 import pandas.core.common as com
 import pandas.core.algorithms as algos
-from pandas.types.generic import ABCDataFrame
+from pandas.core.dtypes.generic import ABCDataFrame
 
 import pandas.compat as compat
 from pandas.compat.numpy import function as nv
@@ -706,7 +706,7 @@ def _downsample(self, how, **kwargs):
             # reset to the new freq
             obj = obj.copy()
             obj.index.freq = self.freq
-            return self._wrap_result(obj)
+            return obj
 
         # do we have a regular frequency
         if ax.freq is not None or ax.inferred_freq is not None:
@@ -777,7 +777,6 @@ def _wrap_result(self, result):
         # convert if needed
         if self.kind == 'period' and not isinstance(result.index, PeriodIndex):
             result.index = result.index.to_period(self.freq)
-
         return result
 
 
diff --git a/pandas/tests/test_resample.py b/pandas/tests/test_resample.py
index 2eee5f4beca45..6a3b21df0f511 100644
--- a/pandas/tests/test_resample.py
+++ b/pandas/tests/test_resample.py
@@ -773,18 +773,8 @@ def test_resample_empty_series(self):
                 expected = s.copy()
                 expected.index = s.index._shallow_copy(freq=freq)
                 assert_index_equal(result.index, expected.index)
-
-                self.assertEqual(result.index.freq, expected.index.freq)
-
-                if (method == 'size' and
-                    isinstance(result.index, PeriodIndex) and
-                        freq in ['M', 'D']):
-                    # GH12871 - TODO: name should propagate, but currently
-                    # doesn't on lower / same frequency with PeriodIndex
-                    assert_series_equal(result, expected, check_dtype=False)
-
-                else:
-                    assert_series_equal(result, expected, check_dtype=False)
+                assert result.index.freq == expected.index.freq
+                assert_series_equal(result, expected, check_dtype=False)
 
     def test_resample_empty_dataframe(self):
         # GH13212
@@ -798,16 +788,16 @@ def test_resample_empty_dataframe(self):
                 result = getattr(f.resample(freq), method)()
                 if method != 'size':
                     expected = f.copy()
-                    assert_equal = assert_frame_equal
+                    assert_type_equal = assert_frame_equal
                 else:
                     # GH14962
                     expected = Series([])
-                    assert_equal = assert_series_equal
+                    assert_type_equal = assert_series_equal
 
                 expected.index = f.index._shallow_copy(freq=freq)
                 assert_index_equal(result.index, expected.index)
                 assert result.index.freq == expected.index.freq
-                assert_frame_equal(result, expected, check_dtype=False)
+                assert_type_equal(result, expected, check_dtype=False)
 
             # test size for GH13212 (currently stays as df)
 

From 44f52be242c797db498e38e35ea74945a1d598c3 Mon Sep 17 00:00:00 2001
From: discort <odiscort@gmail.com>
Date: Tue, 13 Jun 2017 15:48:22 +0300
Subject: [PATCH 6/6] Fixed Jeff's comments

---
 doc/source/whatsnew/v0.21.0.txt | 2 +-
 pandas/core/resample.py         | 3 ++-
 pandas/tests/test_resample.py   | 4 +---
 3 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/doc/source/whatsnew/v0.21.0.txt b/doc/source/whatsnew/v0.21.0.txt
index c9f84b37ad874..56275cda80e57 100644
--- a/doc/source/whatsnew/v0.21.0.txt
+++ b/doc/source/whatsnew/v0.21.0.txt
@@ -112,7 +112,7 @@ Plotting
 
 Groupby/Resample/Rolling
 ^^^^^^^^^^^^^^^^^^^^^^^^
-- Bug in ``resample().size()``. Inconsistent return type on resample of empty DataFrame (:issue:`14962`)
+- Bug in ``DataFrame.resample().size()`` where an empty DataFrame did not return a Series (:issue:`14962`)
 
 
 
diff --git a/pandas/core/resample.py b/pandas/core/resample.py
index f5c615f2b4db9..a8a48624fb885 100644
--- a/pandas/core/resample.py
+++ b/pandas/core/resample.py
@@ -552,7 +552,8 @@ def var(self, ddof=1, *args, **kwargs):
 
     @Appender(GroupBy.size.__doc__)
     def size(self):
-        # It 'seems' special and needs extra handling. GH14962
+        # It's a special case as higher level does return
+        # a copy of 0-len objects. GH14962
         result = self._downsample('size')
         if not len(self.ax) and isinstance(self._selected_obj, ABCDataFrame):
             result = pd.Series([], index=result.index, dtype='int64')
diff --git a/pandas/tests/test_resample.py b/pandas/tests/test_resample.py
index 6a3b21df0f511..15bbd7a9ef5e9 100644
--- a/pandas/tests/test_resample.py
+++ b/pandas/tests/test_resample.py
@@ -788,16 +788,14 @@ def test_resample_empty_dataframe(self):
                 result = getattr(f.resample(freq), method)()
                 if method != 'size':
                     expected = f.copy()
-                    assert_type_equal = assert_frame_equal
                 else:
                     # GH14962
                     expected = Series([])
-                    assert_type_equal = assert_series_equal
 
                 expected.index = f.index._shallow_copy(freq=freq)
                 assert_index_equal(result.index, expected.index)
                 assert result.index.freq == expected.index.freq
-                assert_type_equal(result, expected, check_dtype=False)
+                assert_almost_equal(result, expected, check_dtype=False)
 
             # test size for GH13212 (currently stays as df)