From 3451902344f7f1d97175678f2021277c8f5e879a Mon Sep 17 00:00:00 2001
From: usersblock <thomasly8991@gmail.com>
Date: Tue, 20 Jul 2021 01:52:59 -0400
Subject: [PATCH 01/22] Update test_to_datetime.py

---
 pandas/tests/tools/test_to_datetime.py | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/pandas/tests/tools/test_to_datetime.py b/pandas/tests/tools/test_to_datetime.py
index 9da7951c199ca..349943c6d0b50 100644
--- a/pandas/tests/tools/test_to_datetime.py
+++ b/pandas/tests/tools/test_to_datetime.py
@@ -2530,3 +2530,16 @@ def test_empty_string_datetime_coerce__unit():
     # verify that no exception is raised even when errors='raise' is set
     result = to_datetime([1, ""], unit="s", errors="raise")
     tm.assert_index_equal(expected, result)
+
+
+def test_to_datetime_monotonic_increasing_index():
+    # GH28238
+    # Create date range of 1000 hour periods
+    times = pd.date_range(datetime.now(), periods=1000, freq='h')
+    # Random sort
+    times = times.to_frame(index=False, name='DT').sample(1000)
+    # Divide index integers by 1000
+    times.index = times.index.to_series().astype(float) / 1000
+    # Convert to datetime
+    result = pd.to_datetime(times.iloc[:, 0])
+    assert result.values.dtype == np.dtype('datetime64[ns]')

From 1b528225089d7469f83ddc0e20ce86f750ccfdb2 Mon Sep 17 00:00:00 2001
From: usersblock <thomasly8991@gmail.com>
Date: Tue, 20 Jul 2021 03:33:02 -0400
Subject: [PATCH 02/22] Update test_to_datetime.py

---
 pandas/tests/tools/test_to_datetime.py | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/pandas/tests/tools/test_to_datetime.py b/pandas/tests/tools/test_to_datetime.py
index 349943c6d0b50..d5e90162d671e 100644
--- a/pandas/tests/tools/test_to_datetime.py
+++ b/pandas/tests/tools/test_to_datetime.py
@@ -2535,11 +2535,11 @@ def test_empty_string_datetime_coerce__unit():
 def test_to_datetime_monotonic_increasing_index():
     # GH28238
     # Create date range of 1000 hour periods
-    times = pd.date_range(datetime.now(), periods=1000, freq='h')
+    times = date_range(datetime.now(), periods=1000, freq="h")
     # Random sort
-    times = times.to_frame(index=False, name='DT').sample(1000)
+    times = times.to_frame(index=False, name="DT").sample(1000)
     # Divide index integers by 1000
     times.index = times.index.to_series().astype(float) / 1000
     # Convert to datetime
-    result = pd.to_datetime(times.iloc[:, 0])
-    assert result.values.dtype == np.dtype('datetime64[ns]')
+    result = to_datetime(times.iloc[:, 0])
+    assert result.values.dtype == np.dtype("datetime64[ns]")

From 59d4145c6f62d87bccd13bdc213fffe262903485 Mon Sep 17 00:00:00 2001
From: usersblock <thomasly8991@gmail.com>
Date: Tue, 20 Jul 2021 20:08:02 -0400
Subject: [PATCH 03/22] Update test_to_datetime.py

---
 pandas/tests/tools/test_to_datetime.py | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/pandas/tests/tools/test_to_datetime.py b/pandas/tests/tools/test_to_datetime.py
index d5e90162d671e..a172ecd8e8f56 100644
--- a/pandas/tests/tools/test_to_datetime.py
+++ b/pandas/tests/tools/test_to_datetime.py
@@ -2534,12 +2534,10 @@ def test_empty_string_datetime_coerce__unit():
 
 def test_to_datetime_monotonic_increasing_index():
     # GH28238
-    # Create date range of 1000 hour periods
     times = date_range(datetime.now(), periods=1000, freq="h")
-    # Random sort
     times = times.to_frame(index=False, name="DT").sample(1000)
-    # Divide index integers by 1000
     times.index = times.index.to_series().astype(float) / 1000
-    # Convert to datetime
-    result = to_datetime(times.iloc[:, 0])
-    assert result.values.dtype == np.dtype("datetime64[ns]")
+    converted = to_datetime(times.iloc[:, 0])
+    expected = np.ravel(times.values)
+    result = np.ravel(converted.values)
+    tm.assert_equal(result, expected)

From 763d84ca65fa34dca69f648b43728b137445584c Mon Sep 17 00:00:00 2001
From: usersblock <thomasly8991@gmail.com>
Date: Thu, 22 Jul 2021 16:58:44 -0400
Subject: [PATCH 04/22] Update test_to_datetime.py

---
 pandas/tests/tools/test_to_datetime.py | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/pandas/tests/tools/test_to_datetime.py b/pandas/tests/tools/test_to_datetime.py
index a172ecd8e8f56..7e876e1c1d8c0 100644
--- a/pandas/tests/tools/test_to_datetime.py
+++ b/pandas/tests/tools/test_to_datetime.py
@@ -2532,12 +2532,12 @@ def test_empty_string_datetime_coerce__unit():
     tm.assert_index_equal(expected, result)
 
 
-def test_to_datetime_monotonic_increasing_index():
+@pytest.mark.parametrize("cache", [True, False])
+def test_to_datetime_monotonic_increasing_index(cache):
     # GH28238
-    times = date_range(datetime.now(), periods=1000, freq="h")
-    times = times.to_frame(index=False, name="DT").sample(1000)
+    times = date_range(pd.Timestamp("2002"), periods=3, freq="h")
+    times = times.to_frame(index=False, name="DT").sample()
     times.index = times.index.to_series().astype(float) / 1000
-    converted = to_datetime(times.iloc[:, 0])
-    expected = np.ravel(times.values)
-    result = np.ravel(converted.values)
-    tm.assert_equal(result, expected)
+    result = to_datetime(times.iloc[:, 0], cache=cache)
+    expected = times.iloc[:, 0]
+    tm.assert_series_equal(result, expected)

From 1404f7a55f7642af1801bec4b7862dd699740ede Mon Sep 17 00:00:00 2001
From: usersblock <thomasly8991@gmail.com>
Date: Fri, 23 Jul 2021 14:13:41 -0400
Subject: [PATCH 05/22] Update test_to_datetime.py

---
 pandas/tests/tools/test_to_datetime.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pandas/tests/tools/test_to_datetime.py b/pandas/tests/tools/test_to_datetime.py
index 7e876e1c1d8c0..8f1a918bef4d6 100644
--- a/pandas/tests/tools/test_to_datetime.py
+++ b/pandas/tests/tools/test_to_datetime.py
@@ -2535,8 +2535,8 @@ def test_empty_string_datetime_coerce__unit():
 @pytest.mark.parametrize("cache", [True, False])
 def test_to_datetime_monotonic_increasing_index(cache):
     # GH28238
-    times = date_range(pd.Timestamp("2002"), periods=3, freq="h")
-    times = times.to_frame(index=False, name="DT").sample()
+    times = Series([Timestamp("2002"), Timestamp("2012"), Timestamp("2020")])
+    times = times.to_frame(name="DT").sample(3)
     times.index = times.index.to_series().astype(float) / 1000
     result = to_datetime(times.iloc[:, 0], cache=cache)
     expected = times.iloc[:, 0]

From c649998f35ec4ac6aa67502a10b523372c5c4a44 Mon Sep 17 00:00:00 2001
From: usersblock <thomasly8991@gmail.com>
Date: Fri, 23 Jul 2021 19:26:17 -0400
Subject: [PATCH 06/22] Update test_to_datetime.py

---
 pandas/tests/tools/test_to_datetime.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pandas/tests/tools/test_to_datetime.py b/pandas/tests/tools/test_to_datetime.py
index 8f1a918bef4d6..c0b782354c6f2 100644
--- a/pandas/tests/tools/test_to_datetime.py
+++ b/pandas/tests/tools/test_to_datetime.py
@@ -2535,8 +2535,8 @@ def test_empty_string_datetime_coerce__unit():
 @pytest.mark.parametrize("cache", [True, False])
 def test_to_datetime_monotonic_increasing_index(cache):
     # GH28238
-    times = Series([Timestamp("2002"), Timestamp("2012"), Timestamp("2020")])
-    times = times.to_frame(name="DT").sample(3)
+    times = pd.date_range(pd.Timestamp("1980"), periods=50, freq="YS")
+    times = times.to_frame(index=False, name="DT").sample(50)
     times.index = times.index.to_series().astype(float) / 1000
     result = to_datetime(times.iloc[:, 0], cache=cache)
     expected = times.iloc[:, 0]

From 44645d73f372bd43cb63bb952dead3073a03aaf3 Mon Sep 17 00:00:00 2001
From: usersblock <thomasly8991@gmail.com>
Date: Sat, 24 Jul 2021 01:37:31 -0400
Subject: [PATCH 07/22] Update test_to_datetime.py

---
 pandas/tests/tools/test_to_datetime.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pandas/tests/tools/test_to_datetime.py b/pandas/tests/tools/test_to_datetime.py
index c0b782354c6f2..3a67b8b128050 100644
--- a/pandas/tests/tools/test_to_datetime.py
+++ b/pandas/tests/tools/test_to_datetime.py
@@ -2535,8 +2535,8 @@ def test_empty_string_datetime_coerce__unit():
 @pytest.mark.parametrize("cache", [True, False])
 def test_to_datetime_monotonic_increasing_index(cache):
     # GH28238
-    times = pd.date_range(pd.Timestamp("1980"), periods=50, freq="YS")
-    times = times.to_frame(index=False, name="DT").sample(50)
+    times = date_range(Timestamp("1980"), periods=50, freq="YS")
+    times = times.to_frame(index=False, name="DT").sample(n=50, random_state=1)
     times.index = times.index.to_series().astype(float) / 1000
     result = to_datetime(times.iloc[:, 0], cache=cache)
     expected = times.iloc[:, 0]

From e3cb80c298f3c2bd2988532bbac6a53bf0df493f Mon Sep 17 00:00:00 2001
From: usersblock <thomasly8991@gmail.com>
Date: Sat, 24 Jul 2021 15:07:24 -0400
Subject: [PATCH 08/22] Update test_to_datetime.py

---
 pandas/tests/tools/test_to_datetime.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/pandas/tests/tools/test_to_datetime.py b/pandas/tests/tools/test_to_datetime.py
index 3a67b8b128050..7078661b4568a 100644
--- a/pandas/tests/tools/test_to_datetime.py
+++ b/pandas/tests/tools/test_to_datetime.py
@@ -2535,8 +2535,9 @@ def test_empty_string_datetime_coerce__unit():
 @pytest.mark.parametrize("cache", [True, False])
 def test_to_datetime_monotonic_increasing_index(cache):
     # GH28238
+    cstart = start_caching_at
     times = date_range(Timestamp("1980"), periods=50, freq="YS")
-    times = times.to_frame(index=False, name="DT").sample(n=50, random_state=1)
+    times = times.to_frame(index=False, name="DT").sample(n=cstart, random_state=1)
     times.index = times.index.to_series().astype(float) / 1000
     result = to_datetime(times.iloc[:, 0], cache=cache)
     expected = times.iloc[:, 0]

From 970ed06055ec703159a26af5895127d28f105bc3 Mon Sep 17 00:00:00 2001
From: usersblock <thomasly8991@gmail.com>
Date: Sun, 25 Jul 2021 00:21:41 -0400
Subject: [PATCH 09/22] Update test_to_datetime.py

---
 pandas/tests/tools/test_to_datetime.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/tests/tools/test_to_datetime.py b/pandas/tests/tools/test_to_datetime.py
index 7078661b4568a..7351f50aea8c1 100644
--- a/pandas/tests/tools/test_to_datetime.py
+++ b/pandas/tests/tools/test_to_datetime.py
@@ -2536,7 +2536,7 @@ def test_empty_string_datetime_coerce__unit():
 def test_to_datetime_monotonic_increasing_index(cache):
     # GH28238
     cstart = start_caching_at
-    times = date_range(Timestamp("1980"), periods=50, freq="YS")
+    times = date_range(Timestamp("1980"), periods=cstart, freq="YS")
     times = times.to_frame(index=False, name="DT").sample(n=cstart, random_state=1)
     times.index = times.index.to_series().astype(float) / 1000
     result = to_datetime(times.iloc[:, 0], cache=cache)

From 71be2093e1f71825c73638c99aec0ea047295fed Mon Sep 17 00:00:00 2001
From: usersblock <thomasly8991@gmail.com>
Date: Sun, 15 Aug 2021 19:13:26 -0400
Subject: [PATCH 10/22] Updated Test and fixed nlargest

---
 pandas/core/algorithms.py                    | 9 +++++++--
 pandas/tests/series/methods/test_nlargest.py | 4 ++--
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/pandas/core/algorithms.py b/pandas/core/algorithms.py
index 4f9dd61b8e0da..da7184297fb56 100644
--- a/pandas/core/algorithms.py
+++ b/pandas/core/algorithms.py
@@ -72,6 +72,7 @@
     na_value_for_dtype,
 )
 
+import pandas as pd
 from pandas.core.array_algos.take import take_nd
 from pandas.core.construction import (
     array as pd_array,
@@ -1256,6 +1257,7 @@ def compute(self, method: str) -> Series:
             return self.obj[[]]
 
         dropped = self.obj.dropna()
+        nan_index = self.obj.drop(dropped.index)
 
         if is_extension_array_dtype(dropped.dtype):
             # GH#41816 bc we have dropped NAs above, MaskedArrays can use the
@@ -1272,7 +1274,7 @@ def compute(self, method: str) -> Series:
         # slow method
         if n >= len(self.obj):
             ascending = method == "nsmallest"
-            return dropped.sort_values(ascending=ascending).head(n)
+            return self.obj.sort_values(ascending=ascending).head(n)
 
         # fast method
         new_dtype = dropped.dtype
@@ -1290,6 +1292,8 @@ def compute(self, method: str) -> Series:
         if self.keep == "last":
             arr = arr[::-1]
 
+        nbase = n
+        findex = len(self.obj)
         narr = len(arr)
         n = min(n, narr)
 
@@ -1301,12 +1305,13 @@ def compute(self, method: str) -> Series:
 
         if self.keep != "all":
             inds = inds[:n]
+            findex = nbase
 
         if self.keep == "last":
             # reverse indices
             inds = narr - 1 - inds
 
-        return dropped.iloc[inds]
+        return pd.concat([dropped.iloc[inds],nan_index])[:findex]
 
 
 class SelectNFrame(SelectN):
diff --git a/pandas/tests/series/methods/test_nlargest.py b/pandas/tests/series/methods/test_nlargest.py
index 0efb0663a0327..739fd772c48f1 100644
--- a/pandas/tests/series/methods/test_nlargest.py
+++ b/pandas/tests/series/methods/test_nlargest.py
@@ -127,8 +127,8 @@ def test_nsmallest_nlargest(self, s_main_dtypes_split):
     def test_nlargest_misc(self):
 
         ser = Series([3.0, np.nan, 1, 2, 5])
-        tm.assert_series_equal(ser.nlargest(), ser.iloc[[4, 0, 3, 2]])
-        tm.assert_series_equal(ser.nsmallest(), ser.iloc[[2, 3, 0, 4]])
+        tm.assert_series_equal(ser.nlargest(), ser.iloc[[4, 0, 3, 2, 1]])
+        tm.assert_series_equal(ser.nsmallest(), ser.iloc[[2, 3, 0, 4, 1]])
 
         msg = 'keep must be either "first", "last"'
         with pytest.raises(ValueError, match=msg):

From c5c751c4e521756b0ad454e7c9b4b211a65ba3d8 Mon Sep 17 00:00:00 2001
From: usersblock <thomasly8991@gmail.com>
Date: Sun, 15 Aug 2021 20:11:42 -0400
Subject: [PATCH 11/22] Update algorithms.py

---
 pandas/core/algorithms.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/algorithms.py b/pandas/core/algorithms.py
index da7184297fb56..bbcd1edfea1c1 100644
--- a/pandas/core/algorithms.py
+++ b/pandas/core/algorithms.py
@@ -1311,7 +1311,7 @@ def compute(self, method: str) -> Series:
             # reverse indices
             inds = narr - 1 - inds
 
-        return pd.concat([dropped.iloc[inds],nan_index])[:findex]
+        return pd.concat([dropped.iloc[inds], nan_index])[:findex]
 
 
 class SelectNFrame(SelectN):

From a00fb9e0e77cfebce8bba929233858570d900a86 Mon Sep 17 00:00:00 2001
From: usersblock <thomasly8991@gmail.com>
Date: Sun, 15 Aug 2021 23:56:15 -0400
Subject: [PATCH 12/22] Update algorithms.py

---
 pandas/core/algorithms.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pandas/core/algorithms.py b/pandas/core/algorithms.py
index bbcd1edfea1c1..40e08fd6b691b 100644
--- a/pandas/core/algorithms.py
+++ b/pandas/core/algorithms.py
@@ -72,7 +72,6 @@
     na_value_for_dtype,
 )
 
-import pandas as pd
 from pandas.core.array_algos.take import take_nd
 from pandas.core.construction import (
     array as pd_array,
@@ -1248,6 +1247,7 @@ class SelectNSeries(SelectN):
 
     def compute(self, method: str) -> Series:
 
+        from pandas.core.reshape.concat import concat
         n = self.n
         dtype = self.obj.dtype
         if not self.is_valid_dtype_n_method(dtype):
@@ -1311,7 +1311,7 @@ def compute(self, method: str) -> Series:
             # reverse indices
             inds = narr - 1 - inds
 
-        return pd.concat([dropped.iloc[inds], nan_index])[:findex]
+        return concat([dropped.iloc[inds], nan_index])[:findex]
 
 
 class SelectNFrame(SelectN):

From 6e5c7b09d82d77626963505bb67cc56f3202e32f Mon Sep 17 00:00:00 2001
From: usersblock <thomasly8991@gmail.com>
Date: Mon, 16 Aug 2021 00:10:28 -0400
Subject: [PATCH 13/22] Update algorithms.py

---
 pandas/core/algorithms.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/pandas/core/algorithms.py b/pandas/core/algorithms.py
index 40e08fd6b691b..0765ef0acf7b8 100644
--- a/pandas/core/algorithms.py
+++ b/pandas/core/algorithms.py
@@ -1248,6 +1248,7 @@ class SelectNSeries(SelectN):
     def compute(self, method: str) -> Series:
 
         from pandas.core.reshape.concat import concat
+
         n = self.n
         dtype = self.obj.dtype
         if not self.is_valid_dtype_n_method(dtype):

From a1a9d06abbb8a11baa48dd236c8e94fa75fe3d20 Mon Sep 17 00:00:00 2001
From: usersblock <thomasly8991@gmail.com>
Date: Mon, 16 Aug 2021 20:44:16 -0400
Subject: [PATCH 14/22] Update test_nlargest.py

---
 pandas/tests/frame/methods/test_nlargest.py | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/pandas/tests/frame/methods/test_nlargest.py b/pandas/tests/frame/methods/test_nlargest.py
index 4ce474230b686..a79bef38b6ffe 100644
--- a/pandas/tests/frame/methods/test_nlargest.py
+++ b/pandas/tests/frame/methods/test_nlargest.py
@@ -209,3 +209,17 @@ def test_nlargest_multiindex_column_lookup(self):
         result = df.nlargest(3, ("x", "b"))
         expected = df.iloc[[3, 2, 1]]
         tm.assert_frame_equal(result, expected)
+
+    def test_nlargest_nan_column(self):
+        # GH#43060
+        df = pd.DataFrame(
+            {
+                'grp': [1, 1, 2, 2],
+                'y': [1, 0, 2, 5],
+                'z': [1, 2, np.nan, np.nan]
+            }
+        )
+        dfgrp = df.groupby('grp')
+        result = dfgrp.apply(lambda grp_df: grp_df.nlargest(1, 'z'))
+        expected = dfgrp.apply(lambda x: x.sort_values('z', ascending=False).head(1))
+        tm.assert_frame_equal(result, expected)

From 491d077682199e5d93d30b77275df2f8be66fcd3 Mon Sep 17 00:00:00 2001
From: usersblock <thomasly8991@gmail.com>
Date: Mon, 16 Aug 2021 20:56:47 -0400
Subject: [PATCH 15/22] Update test_nlargest.py

---
 pandas/tests/frame/methods/test_nlargest.py | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/pandas/tests/frame/methods/test_nlargest.py b/pandas/tests/frame/methods/test_nlargest.py
index a79bef38b6ffe..3d73a3974eaaa 100644
--- a/pandas/tests/frame/methods/test_nlargest.py
+++ b/pandas/tests/frame/methods/test_nlargest.py
@@ -213,11 +213,7 @@ def test_nlargest_multiindex_column_lookup(self):
     def test_nlargest_nan_column(self):
         # GH#43060
         df = pd.DataFrame(
-            {
-                'grp': [1, 1, 2, 2],
-                'y': [1, 0, 2, 5],
-                'z': [1, 2, np.nan, np.nan]
-            }
+            {'grp': [1, 1, 2, 2], 'y': [1, 0, 2, 5], 'z': [1, 2, np.nan, np.nan]}
         )
         dfgrp = df.groupby('grp')
         result = dfgrp.apply(lambda grp_df: grp_df.nlargest(1, 'z'))

From 8708cc036518074349d92412860542e618cd13e5 Mon Sep 17 00:00:00 2001
From: usersblock <thomasly8991@gmail.com>
Date: Mon, 16 Aug 2021 21:07:35 -0400
Subject: [PATCH 16/22] Update test_nlargest.py

---
 pandas/tests/frame/methods/test_nlargest.py | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/pandas/tests/frame/methods/test_nlargest.py b/pandas/tests/frame/methods/test_nlargest.py
index 3d73a3974eaaa..12be924bbef44 100644
--- a/pandas/tests/frame/methods/test_nlargest.py
+++ b/pandas/tests/frame/methods/test_nlargest.py
@@ -213,9 +213,9 @@ def test_nlargest_multiindex_column_lookup(self):
     def test_nlargest_nan_column(self):
         # GH#43060
         df = pd.DataFrame(
-            {'grp': [1, 1, 2, 2], 'y': [1, 0, 2, 5], 'z': [1, 2, np.nan, np.nan]}
+            {"grp": [1, 1, 2, 2], "y": [1, 0, 2, 5], "z": [1, 2, np.nan, np.nan]}
         )
-        dfgrp = df.groupby('grp')
-        result = dfgrp.apply(lambda grp_df: grp_df.nlargest(1, 'z'))
-        expected = dfgrp.apply(lambda x: x.sort_values('z', ascending=False).head(1))
+        dfgrp = df.groupby("grp")
+        result = dfgrp.apply(lambda grp_df: grp_df.nlargest(1, "z"))
+        expected = dfgrp.apply(lambda x: x.sort_values("z", ascending=False).head(1))
         tm.assert_frame_equal(result, expected)

From a5cb642fc4850bb783193dd022c8b91dc30b4420 Mon Sep 17 00:00:00 2001
From: usersblock <thomasly8991@gmail.com>
Date: Wed, 25 Aug 2021 04:20:58 -0400
Subject: [PATCH 17/22] Update test_nlargest.py

---
 pandas/tests/frame/methods/test_nlargest.py | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/pandas/tests/frame/methods/test_nlargest.py b/pandas/tests/frame/methods/test_nlargest.py
index 12be924bbef44..1b2db80d782ce 100644
--- a/pandas/tests/frame/methods/test_nlargest.py
+++ b/pandas/tests/frame/methods/test_nlargest.py
@@ -210,12 +210,9 @@ def test_nlargest_multiindex_column_lookup(self):
         expected = df.iloc[[3, 2, 1]]
         tm.assert_frame_equal(result, expected)
 
-    def test_nlargest_nan_column(self):
+    def test_nlargest_nan(self):
         # GH#43060
-        df = pd.DataFrame(
-            {"grp": [1, 1, 2, 2], "y": [1, 0, 2, 5], "z": [1, 2, np.nan, np.nan]}
-        )
-        dfgrp = df.groupby("grp")
-        result = dfgrp.apply(lambda grp_df: grp_df.nlargest(1, "z"))
-        expected = dfgrp.apply(lambda x: x.sort_values("z", ascending=False).head(1))
+        df = pd.DataFrame([np.nan, np.nan, 0, 1, 2, 3])
+        result = df.nlargest(5, 0)
+        expected = df.sort_values(0, ascending=False).head(5)
         tm.assert_frame_equal(result, expected)

From 7d2aac441be75cdbff804661e187efd6cac4b9fc Mon Sep 17 00:00:00 2001
From: usersblock <thomasly8991@gmail.com>
Date: Fri, 27 Aug 2021 03:50:10 -0400
Subject: [PATCH 18/22] Updated test_nlargest and docs

---
 doc/source/whatsnew/v1.4.0.rst               | 2 +-
 pandas/tests/series/methods/test_nlargest.py | 8 ++++++--
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/doc/source/whatsnew/v1.4.0.rst b/doc/source/whatsnew/v1.4.0.rst
index f0af60f80edd5..90d71434bc39f 100644
--- a/doc/source/whatsnew/v1.4.0.rst
+++ b/doc/source/whatsnew/v1.4.0.rst
@@ -288,7 +288,7 @@ Indexing
 - Bug in :meth:`Index.get_indexer_non_unique` when index contains multiple ``np.nan`` (:issue:`35392`)
 - Bug in :meth:`DataFrame.query` did not handle the degree sign in a backticked column name, such as \`Temp(°C)\`, used in an expression to query a dataframe (:issue:`42826`)
 - Bug in :meth:`DataFrame.drop` where the error message did not show missing labels with commas when raising ``KeyError`` (:issue:`42881`)
--
+- Bug in :meth:`DataFrame.nlargest` and :meth:`Series.nlargest` where sorted result did not count indexes containing ``np.nan``
 
 Missing
 ^^^^^^^
diff --git a/pandas/tests/series/methods/test_nlargest.py b/pandas/tests/series/methods/test_nlargest.py
index 739fd772c48f1..8b0779c44bf4c 100644
--- a/pandas/tests/series/methods/test_nlargest.py
+++ b/pandas/tests/series/methods/test_nlargest.py
@@ -127,8 +127,12 @@ def test_nsmallest_nlargest(self, s_main_dtypes_split):
     def test_nlargest_misc(self):
 
         ser = Series([3.0, np.nan, 1, 2, 5])
-        tm.assert_series_equal(ser.nlargest(), ser.iloc[[4, 0, 3, 2, 1]])
-        tm.assert_series_equal(ser.nsmallest(), ser.iloc[[2, 3, 0, 4, 1]])
+        result = ser.nlargest()
+        expected = ser.iloc[[4, 0, 3, 2, 1]]
+        tm.assert_series_equal(result, expected)
+        result = ser.nsmallest()
+        expected = ser.iloc[[2, 3, 0, 4, 1]]
+        tm.assert_series_equal(result, expected)
 
         msg = 'keep must be either "first", "last"'
         with pytest.raises(ValueError, match=msg):

From 2d0931f15fe43455e1484aa13104d95fa84c5151 Mon Sep 17 00:00:00 2001
From: usersblock <thomasly8991@gmail.com>
Date: Fri, 27 Aug 2021 13:25:14 -0400
Subject: [PATCH 19/22] Update v1.4.0.rst

---
 doc/source/whatsnew/v1.4.0.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/source/whatsnew/v1.4.0.rst b/doc/source/whatsnew/v1.4.0.rst
index 90d71434bc39f..b1752a506c486 100644
--- a/doc/source/whatsnew/v1.4.0.rst
+++ b/doc/source/whatsnew/v1.4.0.rst
@@ -288,7 +288,7 @@ Indexing
 - Bug in :meth:`Index.get_indexer_non_unique` when index contains multiple ``np.nan`` (:issue:`35392`)
 - Bug in :meth:`DataFrame.query` did not handle the degree sign in a backticked column name, such as \`Temp(°C)\`, used in an expression to query a dataframe (:issue:`42826`)
 - Bug in :meth:`DataFrame.drop` where the error message did not show missing labels with commas when raising ``KeyError`` (:issue:`42881`)
-- Bug in :meth:`DataFrame.nlargest` and :meth:`Series.nlargest` where sorted result did not count indexes containing ``np.nan``
+- Bug in :meth:`DataFrame.nlargest` and :meth:`Series.nlargest` where sorted result did not count indexes containing ``np.nan`` (:issue:`28984`)
 
 Missing
 ^^^^^^^

From ca3af2477911c5cb59af43dde601229a3f616357 Mon Sep 17 00:00:00 2001
From: usersblock <thomasly8991@gmail.com>
Date: Fri, 3 Sep 2021 03:24:28 -0400
Subject: [PATCH 20/22] Update test_apply.py

---
 pandas/tests/groupby/test_apply.py | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/pandas/tests/groupby/test_apply.py b/pandas/tests/groupby/test_apply.py
index 25529e65118c8..f0767cb566e29 100644
--- a/pandas/tests/groupby/test_apply.py
+++ b/pandas/tests/groupby/test_apply.py
@@ -1150,3 +1150,15 @@ def test_doctest_example2():
         {"B": [1.0, 0.0], "C": [2.0, 0.0]}, index=Index(["a", "b"], name="A")
     )
     tm.assert_frame_equal(result, expected)
+
+
+@pytest.mark.parametrize("dropna", [True, False])
+def test_apply_na(dropna):
+    # GH#28984
+    df = pd.DataFrame(
+        {"grp": [1, 1, 2, 2], "y": [1, 0, 2, 5], "z": [1, 2, np.nan, np.nan]}
+    )
+    dfgrp = df.groupby("grp", dropna=dropna)
+    result = dfgrp.apply(lambda grp_df: grp_df.nlargest(1, "z"))
+    expected = dfgrp.apply(lambda x: x.sort_values("z", ascending=False).head(1))
+    tm.assert_frame_equal(result, expected)

From 80d4fcbcac638f5ce3aab0594832141c140fe841 Mon Sep 17 00:00:00 2001
From: usersblock <thomasly8991@gmail.com>
Date: Fri, 3 Sep 2021 03:54:43 -0400
Subject: [PATCH 21/22] Update test_apply.py

---
 pandas/tests/groupby/test_apply.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/tests/groupby/test_apply.py b/pandas/tests/groupby/test_apply.py
index f0767cb566e29..0330bc0203185 100644
--- a/pandas/tests/groupby/test_apply.py
+++ b/pandas/tests/groupby/test_apply.py
@@ -1155,7 +1155,7 @@ def test_doctest_example2():
 @pytest.mark.parametrize("dropna", [True, False])
 def test_apply_na(dropna):
     # GH#28984
-    df = pd.DataFrame(
+    df = DataFrame(
         {"grp": [1, 1, 2, 2], "y": [1, 0, 2, 5], "z": [1, 2, np.nan, np.nan]}
     )
     dfgrp = df.groupby("grp", dropna=dropna)

From 5717466e2546f3ae3ccf27a42c7ae89db3b4a067 Mon Sep 17 00:00:00 2001
From: usersblock <thomasly8991@gmail.com>
Date: Tue, 7 Sep 2021 03:41:37 -0400
Subject: [PATCH 22/22] Update algorithms.py

---
 pandas/core/algorithms.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/algorithms.py b/pandas/core/algorithms.py
index 0765ef0acf7b8..0e986aa6afb5d 100644
--- a/pandas/core/algorithms.py
+++ b/pandas/core/algorithms.py
@@ -1312,7 +1312,7 @@ def compute(self, method: str) -> Series:
             # reverse indices
             inds = narr - 1 - inds
 
-        return concat([dropped.iloc[inds], nan_index])[:findex]
+        return concat([dropped.iloc[inds], nan_index]).iloc[:findex]
 
 
 class SelectNFrame(SelectN):