From 3dd89877f0beb29788ce81f6f349214157b8384d Mon Sep 17 00:00:00 2001
From: Trevor Serrao <trevorserrao@gmail.com>
Date: Fri, 28 Jun 2024 13:30:42 -0500
Subject: [PATCH 1/7] add adjust parameter to the ewma variable times test. Add
 tests for disallowed decay-specification parameters when times is specified
 and adjust=False

---
 pandas/tests/window/test_ewm.py | 38 +++++++++++++++++++++++++++------
 1 file changed, 31 insertions(+), 7 deletions(-)

diff --git a/pandas/tests/window/test_ewm.py b/pandas/tests/window/test_ewm.py
index 35c896dc0090b..8023a7fa99966 100644
--- a/pandas/tests/window/test_ewm.py
+++ b/pandas/tests/window/test_ewm.py
@@ -102,7 +102,8 @@ def test_ewma_with_times_equal_spacing(halflife_with_times, times, min_periods):
     tm.assert_frame_equal(result, expected)
 
 
-def test_ewma_with_times_variable_spacing(tz_aware_fixture, unit):
+def test_ewma_with_times_variable_spacing(tz_aware_fixture, unit, adjust):
+    #GH 54328
     tz = tz_aware_fixture
     halflife = "23 days"
     times = (
@@ -112,8 +113,11 @@ def test_ewma_with_times_variable_spacing(tz_aware_fixture, unit):
     )
     data = np.arange(3)
     df = DataFrame(data)
-    result = df.ewm(halflife=halflife, times=times).mean()
-    expected = DataFrame([0.0, 0.5674161888241773, 1.545239952073459])
+    result = df.ewm(halflife=halflife, times=times, adjust=adjust).mean()
+    if adjust:
+        expected = DataFrame([0.0, 0.5674161888241773, 1.545239952073459])
+    else:
+        expected = DataFrame([0.0, 0.23762518642226227, 1.534926369128742])
     tm.assert_frame_equal(result, expected)
 
 
@@ -148,13 +152,33 @@ def test_ewm_getitem_attributes_retained(arg, adjust, ignore_na):
     assert result == expected
 
 
-def test_ewma_times_adjust_false_raises():
-    # GH 40098
+def test_ewma_times_adjust_false_with_disallowed_com():
+    # GH 54328
+    with pytest.raises(
+            NotImplementedError, match='None of com, span, or alpha can be specified if times is provided and adjust=False'
+    ):
+        Series(range(1)).ewm(
+            0.1, adjust=False, times=date_range("2000", freq="D", periods=1), halflife='1D'
+        )
+
+
+def test_ewma_times_adjust_false_with_disallowed_alpha():
+    # GH 54328
+    with pytest.raises(
+            NotImplementedError, match='None of com, span, or alpha can be specified if times is provided and adjust=False'
+    ):
+        Series(range(1)).ewm(
+            0.1, adjust=False, times=date_range("2000", freq="D", periods=1), alpha=0.5, halflife='1D'
+        )
+
+
+def test_ewma_times_adjust_false_with_disallowed_span():
+    # GH 54328
     with pytest.raises(
-        NotImplementedError, match="times is not supported with adjust=False."
+            NotImplementedError, match='None of com, span, or alpha can be specified if times is provided and adjust=False'
     ):
         Series(range(1)).ewm(
-            0.1, adjust=False, times=date_range("2000", freq="D", periods=1)
+            0.1, adjust=False, times=date_range("2000", freq="D", periods=1), span=10, halflife='1D'
         )
 
 

From 5992c3e08b82ad4aeefbc27883f81c63eb0ce2ff Mon Sep 17 00:00:00 2001
From: Trevor Serrao <trevorserrao@gmail.com>
Date: Fri, 28 Jun 2024 13:31:15 -0500
Subject: [PATCH 2/7] allow adjust=False when times is provided

---
 pandas/core/window/ewm.py | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/pandas/core/window/ewm.py b/pandas/core/window/ewm.py
index b2855ff1f4048..06b474982f30e 100644
--- a/pandas/core/window/ewm.py
+++ b/pandas/core/window/ewm.py
@@ -134,8 +134,10 @@ class ExponentialMovingWindow(BaseWindow):
     Provide exponentially weighted (EW) calculations.
 
     Exactly one of ``com``, ``span``, ``halflife``, or ``alpha`` must be
-    provided if ``times`` is not provided. If ``times`` is provided,
+    provided if ``times`` is not provided. If ``times`` is provided and ``adjust=True``,
     ``halflife`` and one of ``com``, ``span`` or ``alpha`` may be provided.
+    If ``times`` is provided and ``adjust=False``, ``halflife`` must be the only
+    provided decay-specification parameter.
 
     Parameters
     ----------
@@ -358,8 +360,6 @@ def __init__(
         self.ignore_na = ignore_na
         self.times = times
         if self.times is not None:
-            if not self.adjust:
-                raise NotImplementedError("times is not supported with adjust=False.")
             times_dtype = getattr(self.times, "dtype", None)
             if not (
                 is_datetime64_dtype(times_dtype)
@@ -376,6 +376,9 @@ def __init__(
             # Halflife is no longer applicable when calculating COM
             # But allow COM to still be calculated if the user passes other decay args
             if common.count_not_none(self.com, self.span, self.alpha) > 0:
+                if not self.adjust:
+                    raise NotImplementedError('None of com, span, or alpha can be specified if '
+                                              'times is provided and adjust=False')
                 self._com = get_center_of_mass(self.com, self.span, None, self.alpha)
             else:
                 self._com = 1.0

From fa1447aa40a0b31d6bbf50ff87f80679cd908b68 Mon Sep 17 00:00:00 2001
From: Trevor Serrao <trevorserrao@gmail.com>
Date: Fri, 28 Jun 2024 13:33:07 -0500
Subject: [PATCH 3/7] re-calculate alpha each iteration for irregular-spaced
 time series

---
 pandas/_libs/window/aggregations.pyx | 3 +++
 pandas/core/window/numba_.py         | 6 ++++++
 2 files changed, 9 insertions(+)

diff --git a/pandas/_libs/window/aggregations.pyx b/pandas/_libs/window/aggregations.pyx
index 6365c030b695b..139c2cf18d5f0 100644
--- a/pandas/_libs/window/aggregations.pyx
+++ b/pandas/_libs/window/aggregations.pyx
@@ -1813,6 +1813,9 @@ def ewm(const float64_t[:] vals, const int64_t[:] start, const int64_t[:] end,
                             if normalize:
                                 # avoid numerical errors on constant series
                                 if weighted != cur:
+                                    if not adjust and com == 1:
+                                        # update alpha "on the fly" for irregular-interval time series
+                                        new_wt = 1. - old_wt
                                     weighted = old_wt * weighted + new_wt * cur
                                     weighted /= (old_wt + new_wt)
                                 if adjust:
diff --git a/pandas/core/window/numba_.py b/pandas/core/window/numba_.py
index 621b0f2c0f2d8..4a20ef9c4468b 100644
--- a/pandas/core/window/numba_.py
+++ b/pandas/core/window/numba_.py
@@ -149,6 +149,9 @@ def ewm(
                             # note that len(deltas) = len(vals) - 1 and deltas[i]
                             # is to be used in conjunction with vals[i+1]
                             old_wt *= old_wt_factor ** deltas[start + j - 1]
+                            if not adjust and com == 1:
+                                # update alpha "on the fly" for irregular-interval time series
+                                new_wt = 1. - old_wt
                         else:
                             weighted = old_wt_factor * weighted
                         if is_observation:
@@ -324,6 +327,9 @@ def ewm_table(
                             # note that len(deltas) = len(vals) - 1 and deltas[i]
                             # is to be used in conjunction with vals[i+1]
                             old_wt[j] *= old_wt_factor ** deltas[i - 1]
+                            if not adjust and com == 1:
+                                # update alpha "on the fly" for irregular-interval time series
+                                new_wt = 1. - old_wt[j]
                         else:
                             weighted[j] = old_wt_factor * weighted[j]
                         if is_observations[j]:

From f64d32e9c3ebaafd3c975532d4685c1e06bdb4ef Mon Sep 17 00:00:00 2001
From: Trevor Serrao <trevorserrao@gmail.com>
Date: Fri, 28 Jun 2024 14:31:55 -0500
Subject: [PATCH 4/7] whatsnew entry for allowing adjust=False with times

---
 doc/source/whatsnew/v3.0.0.rst | 1 +
 1 file changed, 1 insertion(+)

diff --git a/doc/source/whatsnew/v3.0.0.rst b/doc/source/whatsnew/v3.0.0.rst
index 130ccded72859..138743882bd5a 100644
--- a/doc/source/whatsnew/v3.0.0.rst
+++ b/doc/source/whatsnew/v3.0.0.rst
@@ -48,6 +48,7 @@ Other enhancements
 - :meth:`Series.plot` now correctly handle the ``ylabel`` parameter for pie charts, allowing for explicit control over the y-axis label (:issue:`58239`)
 - Restore support for reading Stata 104-format and enable reading 103-format dta files (:issue:`58554`)
 - Support reading Stata 110-format (Stata 7) dta files (:issue:`47176`)
+- :meth:`DataFrame.ewm` now allows ``adjust=False`` when ``times`` is provided (:issue:`54328`)
 
 .. ---------------------------------------------------------------------------
 .. _whatsnew_300.notable_bug_fixes:

From f1d8a6307a8c942cb7d3f35c318e1ef801871583 Mon Sep 17 00:00:00 2001
From: Trevor Serrao <trevorserrao@gmail.com>
Date: Fri, 28 Jun 2024 15:01:01 -0500
Subject: [PATCH 5/7] pre-commit style fixes

---
 doc/source/whatsnew/v3.0.0.rst  |  2 +-
 pandas/core/window/ewm.py       |  6 ++++--
 pandas/core/window/numba_.py    |  4 ++--
 pandas/tests/window/test_ewm.py | 28 +++++++++++++++++++++-------
 4 files changed, 28 insertions(+), 12 deletions(-)

diff --git a/doc/source/whatsnew/v3.0.0.rst b/doc/source/whatsnew/v3.0.0.rst
index 138743882bd5a..816185c428bda 100644
--- a/doc/source/whatsnew/v3.0.0.rst
+++ b/doc/source/whatsnew/v3.0.0.rst
@@ -42,13 +42,13 @@ Other enhancements
 - :func:`DataFrame.to_excel` argument ``merge_cells`` now accepts a value of ``"columns"`` to only merge :class:`MultiIndex` column header header cells (:issue:`35384`)
 - :meth:`DataFrame.corrwith` now accepts ``min_periods`` as optional arguments, as in :meth:`DataFrame.corr` and :meth:`Series.corr` (:issue:`9490`)
 - :meth:`DataFrame.cummin`, :meth:`DataFrame.cummax`, :meth:`DataFrame.cumprod` and :meth:`DataFrame.cumsum` methods now have a ``numeric_only`` parameter (:issue:`53072`)
+- :meth:`DataFrame.ewm` now allows ``adjust=False`` when ``times`` is provided (:issue:`54328`)
 - :meth:`DataFrame.fillna` and :meth:`Series.fillna` can now accept ``value=None``; for non-object dtype the corresponding NA value will be used (:issue:`57723`)
 - :meth:`DataFrame.pivot_table` and :func:`pivot_table` now allow the passing of keyword arguments to ``aggfunc`` through ``**kwargs`` (:issue:`57884`)
 - :meth:`Series.cummin` and :meth:`Series.cummax` now supports :class:`CategoricalDtype` (:issue:`52335`)
 - :meth:`Series.plot` now correctly handle the ``ylabel`` parameter for pie charts, allowing for explicit control over the y-axis label (:issue:`58239`)
 - Restore support for reading Stata 104-format and enable reading 103-format dta files (:issue:`58554`)
 - Support reading Stata 110-format (Stata 7) dta files (:issue:`47176`)
-- :meth:`DataFrame.ewm` now allows ``adjust=False`` when ``times`` is provided (:issue:`54328`)
 
 .. ---------------------------------------------------------------------------
 .. _whatsnew_300.notable_bug_fixes:
diff --git a/pandas/core/window/ewm.py b/pandas/core/window/ewm.py
index 06b474982f30e..43a3c03b6cef9 100644
--- a/pandas/core/window/ewm.py
+++ b/pandas/core/window/ewm.py
@@ -377,8 +377,10 @@ def __init__(
             # But allow COM to still be calculated if the user passes other decay args
             if common.count_not_none(self.com, self.span, self.alpha) > 0:
                 if not self.adjust:
-                    raise NotImplementedError('None of com, span, or alpha can be specified if '
-                                              'times is provided and adjust=False')
+                    raise NotImplementedError(
+                        "None of com, span, or alpha can be specified if "
+                        "times is provided and adjust=False"
+                    )
                 self._com = get_center_of_mass(self.com, self.span, None, self.alpha)
             else:
                 self._com = 1.0
diff --git a/pandas/core/window/numba_.py b/pandas/core/window/numba_.py
index 4a20ef9c4468b..2a0a5d8391ce2 100644
--- a/pandas/core/window/numba_.py
+++ b/pandas/core/window/numba_.py
@@ -151,7 +151,7 @@ def ewm(
                             old_wt *= old_wt_factor ** deltas[start + j - 1]
                             if not adjust and com == 1:
                                 # update alpha "on the fly" for irregular-interval time series
-                                new_wt = 1. - old_wt
+                                new_wt = 1.0 - old_wt
                         else:
                             weighted = old_wt_factor * weighted
                         if is_observation:
@@ -329,7 +329,7 @@ def ewm_table(
                             old_wt[j] *= old_wt_factor ** deltas[i - 1]
                             if not adjust and com == 1:
                                 # update alpha "on the fly" for irregular-interval time series
-                                new_wt = 1. - old_wt[j]
+                                new_wt = 1.0 - old_wt[j]
                         else:
                             weighted[j] = old_wt_factor * weighted[j]
                         if is_observations[j]:
diff --git a/pandas/tests/window/test_ewm.py b/pandas/tests/window/test_ewm.py
index 8023a7fa99966..a68afc2dd8502 100644
--- a/pandas/tests/window/test_ewm.py
+++ b/pandas/tests/window/test_ewm.py
@@ -103,7 +103,7 @@ def test_ewma_with_times_equal_spacing(halflife_with_times, times, min_periods):
 
 
 def test_ewma_with_times_variable_spacing(tz_aware_fixture, unit, adjust):
-    #GH 54328
+    # GH 54328
     tz = tz_aware_fixture
     halflife = "23 days"
     times = (
@@ -155,30 +155,44 @@ def test_ewm_getitem_attributes_retained(arg, adjust, ignore_na):
 def test_ewma_times_adjust_false_with_disallowed_com():
     # GH 54328
     with pytest.raises(
-            NotImplementedError, match='None of com, span, or alpha can be specified if times is provided and adjust=False'
+        NotImplementedError,
+        match="None of com, span, or alpha can be specified if times is provided and adjust=False",
     ):
         Series(range(1)).ewm(
-            0.1, adjust=False, times=date_range("2000", freq="D", periods=1), halflife='1D'
+            0.1,
+            adjust=False,
+            times=date_range("2000", freq="D", periods=1),
+            halflife="1D",
         )
 
 
 def test_ewma_times_adjust_false_with_disallowed_alpha():
     # GH 54328
     with pytest.raises(
-            NotImplementedError, match='None of com, span, or alpha can be specified if times is provided and adjust=False'
+        NotImplementedError,
+        match="None of com, span, or alpha can be specified if times is provided and adjust=False",
     ):
         Series(range(1)).ewm(
-            0.1, adjust=False, times=date_range("2000", freq="D", periods=1), alpha=0.5, halflife='1D'
+            0.1,
+            adjust=False,
+            times=date_range("2000", freq="D", periods=1),
+            alpha=0.5,
+            halflife="1D",
         )
 
 
 def test_ewma_times_adjust_false_with_disallowed_span():
     # GH 54328
     with pytest.raises(
-            NotImplementedError, match='None of com, span, or alpha can be specified if times is provided and adjust=False'
+        NotImplementedError,
+        match="None of com, span, or alpha can be specified if times is provided and adjust=False",
     ):
         Series(range(1)).ewm(
-            0.1, adjust=False, times=date_range("2000", freq="D", periods=1), span=10, halflife='1D'
+            0.1,
+            adjust=False,
+            times=date_range("2000", freq="D", periods=1),
+            span=10,
+            halflife="1D",
         )
 
 

From 33f2054dd52f93f6956d341a581d7558f1b70d6a Mon Sep 17 00:00:00 2001
From: Trevor Serrao <trevorserrao@gmail.com>
Date: Tue, 2 Jul 2024 11:53:58 -0500
Subject: [PATCH 6/7] reduce line lengths to comply with pre-commit

---
 pandas/core/window/numba_.py    | 4 ++--
 pandas/tests/window/test_ewm.py | 9 ++++++---
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/pandas/core/window/numba_.py b/pandas/core/window/numba_.py
index 2a0a5d8391ce2..171d3bc1d1c35 100644
--- a/pandas/core/window/numba_.py
+++ b/pandas/core/window/numba_.py
@@ -150,7 +150,7 @@ def ewm(
                             # is to be used in conjunction with vals[i+1]
                             old_wt *= old_wt_factor ** deltas[start + j - 1]
                             if not adjust and com == 1:
-                                # update alpha "on the fly" for irregular-interval time series
+                                # update in case of irregular-interval time series
                                 new_wt = 1.0 - old_wt
                         else:
                             weighted = old_wt_factor * weighted
@@ -328,7 +328,7 @@ def ewm_table(
                             # is to be used in conjunction with vals[i+1]
                             old_wt[j] *= old_wt_factor ** deltas[i - 1]
                             if not adjust and com == 1:
-                                # update alpha "on the fly" for irregular-interval time series
+                                # update in case of irregular-interval time series
                                 new_wt = 1.0 - old_wt[j]
                         else:
                             weighted[j] = old_wt_factor * weighted[j]
diff --git a/pandas/tests/window/test_ewm.py b/pandas/tests/window/test_ewm.py
index a68afc2dd8502..02646bd3399d4 100644
--- a/pandas/tests/window/test_ewm.py
+++ b/pandas/tests/window/test_ewm.py
@@ -156,7 +156,8 @@ def test_ewma_times_adjust_false_with_disallowed_com():
     # GH 54328
     with pytest.raises(
         NotImplementedError,
-        match="None of com, span, or alpha can be specified if times is provided and adjust=False",
+        match=("None of com, span, or alpha can be specified "
+               "if times is provided and adjust=False"),
     ):
         Series(range(1)).ewm(
             0.1,
@@ -170,7 +171,8 @@ def test_ewma_times_adjust_false_with_disallowed_alpha():
     # GH 54328
     with pytest.raises(
         NotImplementedError,
-        match="None of com, span, or alpha can be specified if times is provided and adjust=False",
+        match=("None of com, span, or alpha can be specified "
+               "if times is provided and adjust=False"),
     ):
         Series(range(1)).ewm(
             0.1,
@@ -185,7 +187,8 @@ def test_ewma_times_adjust_false_with_disallowed_span():
     # GH 54328
     with pytest.raises(
         NotImplementedError,
-        match="None of com, span, or alpha can be specified if times is provided and adjust=False",
+        match=("None of com, span, or alpha can be specified "
+               "if times is provided and adjust=False"),
     ):
         Series(range(1)).ewm(
             0.1,

From 5ca8b17c2bdb7077a74312883aeba6fcdebd29bd Mon Sep 17 00:00:00 2001
From: Trevor Serrao <trevorserrao@gmail.com>
Date: Tue, 2 Jul 2024 12:16:20 -0500
Subject: [PATCH 7/7] reduce line lengths and apply ruff-reformat changes

---
 pandas/_libs/window/aggregations.pyx |  2 +-
 pandas/tests/window/test_ewm.py      | 18 ++++++++++++------
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/pandas/_libs/window/aggregations.pyx b/pandas/_libs/window/aggregations.pyx
index 139c2cf18d5f0..5b9ee095d4643 100644
--- a/pandas/_libs/window/aggregations.pyx
+++ b/pandas/_libs/window/aggregations.pyx
@@ -1814,7 +1814,7 @@ def ewm(const float64_t[:] vals, const int64_t[:] start, const int64_t[:] end,
                                 # avoid numerical errors on constant series
                                 if weighted != cur:
                                     if not adjust and com == 1:
-                                        # update alpha "on the fly" for irregular-interval time series
+                                        # update in case of irregular-interval series
                                         new_wt = 1. - old_wt
                                     weighted = old_wt * weighted + new_wt * cur
                                     weighted /= (old_wt + new_wt)
diff --git a/pandas/tests/window/test_ewm.py b/pandas/tests/window/test_ewm.py
index 02646bd3399d4..4ea6c805a2ee4 100644
--- a/pandas/tests/window/test_ewm.py
+++ b/pandas/tests/window/test_ewm.py
@@ -156,8 +156,10 @@ def test_ewma_times_adjust_false_with_disallowed_com():
     # GH 54328
     with pytest.raises(
         NotImplementedError,
-        match=("None of com, span, or alpha can be specified "
-               "if times is provided and adjust=False"),
+        match=(
+            "None of com, span, or alpha can be specified "
+            "if times is provided and adjust=False"
+        ),
     ):
         Series(range(1)).ewm(
             0.1,
@@ -171,8 +173,10 @@ def test_ewma_times_adjust_false_with_disallowed_alpha():
     # GH 54328
     with pytest.raises(
         NotImplementedError,
-        match=("None of com, span, or alpha can be specified "
-               "if times is provided and adjust=False"),
+        match=(
+            "None of com, span, or alpha can be specified "
+            "if times is provided and adjust=False"
+        ),
     ):
         Series(range(1)).ewm(
             0.1,
@@ -187,8 +191,10 @@ def test_ewma_times_adjust_false_with_disallowed_span():
     # GH 54328
     with pytest.raises(
         NotImplementedError,
-        match=("None of com, span, or alpha can be specified "
-               "if times is provided and adjust=False"),
+        match=(
+            "None of com, span, or alpha can be specified "
+            "if times is provided and adjust=False"
+        ),
     ):
         Series(range(1)).ewm(
             0.1,