From 4bb68ed3736dc95d2766ef40cd75845e2a7f3c1e Mon Sep 17 00:00:00 2001
From: luke <2736230899@qq.com>
Date: Sun, 15 Jan 2023 14:12:37 +0800
Subject: [PATCH 1/4] TST: test-groupby-method-drop-na

---
 pandas/tests/groupby/test_groupby.py | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/pandas/tests/groupby/test_groupby.py b/pandas/tests/groupby/test_groupby.py
index 5384b228850f4..cec702bcb472d 100644
--- a/pandas/tests/groupby/test_groupby.py
+++ b/pandas/tests/groupby/test_groupby.py
@@ -2846,3 +2846,12 @@ def test_sum_of_booleans(n):
     result = df.groupby("groupby_col").sum()
     expected = DataFrame({"bool": [n]}, index=Index([1], name="groupby_col"))
     tm.assert_frame_equal(result, expected)
+
+
+@pytest.mark.parametrize("method, n", [("head", 1), ("nth", 0)])
+def test_groupby_method_drop_na(method, n):
+    # GH 21755
+    df = DataFrame({"A": ["a", np.nan, "b", np.nan, "c"], "B": range(5)})
+    result = df.groupby("A").agg(method, n=n)
+    expected = DataFrame({"A": ["a", "b", "c"], "B": [0, 2, 4]}, index=[0, 2, 4])
+    tm.assert_frame_equal(result, expected)

From d29901958cdfab3214c7c1ce6e4f107502ecf479 Mon Sep 17 00:00:00 2001
From: luke <2736230899@qq.com>
Date: Sun, 15 Jan 2023 20:14:02 +0800
Subject: [PATCH 2/4] add first last tail

---
 pandas/tests/groupby/test_groupby.py | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/pandas/tests/groupby/test_groupby.py b/pandas/tests/groupby/test_groupby.py
index cec702bcb472d..d5ccae1f8d642 100644
--- a/pandas/tests/groupby/test_groupby.py
+++ b/pandas/tests/groupby/test_groupby.py
@@ -2848,10 +2848,20 @@ def test_sum_of_booleans(n):
     tm.assert_frame_equal(result, expected)
 
 
-@pytest.mark.parametrize("method, n", [("head", 1), ("nth", 0)])
-def test_groupby_method_drop_na(method, n):
+@pytest.mark.parametrize("method", ["head", "tail", "nth", "first", "last"])
+def test_groupby_method_drop_na(method):
     # GH 21755
     df = DataFrame({"A": ["a", np.nan, "b", np.nan, "c"], "B": range(5)})
-    result = df.groupby("A").agg(method, n=n)
-    expected = DataFrame({"A": ["a", "b", "c"], "B": [0, 2, 4]}, index=[0, 2, 4])
+
+    if method == "nth":
+        result = df.groupby("A").agg(method, n=0)
+    else:
+        result = df.groupby("A").agg(method)
+
+    if method in ["first", "last"]:
+        expected = DataFrame({"B": [0, 2, 4]})
+        index = Series(["a", "b", "c"], name="A")
+        expected.set_index(index, inplace=True)
+    else:
+        expected = DataFrame({"A": ["a", "b", "c"], "B": [0, 2, 4]}, index=[0, 2, 4])
     tm.assert_frame_equal(result, expected)

From f0fe53674958ca82482cd603cd6bd4f796a4ab54 Mon Sep 17 00:00:00 2001
From: luke <2736230899@qq.com>
Date: Mon, 16 Jan 2023 11:15:39 +0800
Subject: [PATCH 3/4] construct DataFrame in one line

---
 pandas/tests/groupby/test_groupby.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/pandas/tests/groupby/test_groupby.py b/pandas/tests/groupby/test_groupby.py
index d5ccae1f8d642..e17d6b7c4feb5 100644
--- a/pandas/tests/groupby/test_groupby.py
+++ b/pandas/tests/groupby/test_groupby.py
@@ -2859,9 +2859,9 @@ def test_groupby_method_drop_na(method):
         result = df.groupby("A").agg(method)
 
     if method in ["first", "last"]:
-        expected = DataFrame({"B": [0, 2, 4]})
-        index = Series(["a", "b", "c"], name="A")
-        expected.set_index(index, inplace=True)
+        expected = DataFrame({"B": [0, 2, 4]}).set_index(
+            Series(["a", "b", "c"], name="A")
+        )
     else:
         expected = DataFrame({"A": ["a", "b", "c"], "B": [0, 2, 4]}, index=[0, 2, 4])
     tm.assert_frame_equal(result, expected)

From e4fce3a50abb41dce44f59886fdb7c86b346f9b4 Mon Sep 17 00:00:00 2001
From: luke <2736230899@qq.com>
Date: Tue, 17 Jan 2023 12:07:58 +0800
Subject: [PATCH 4/4] use actual func instead of agg

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

diff --git a/pandas/tests/groupby/test_groupby.py b/pandas/tests/groupby/test_groupby.py
index e17d6b7c4feb5..b4a243671e287 100644
--- a/pandas/tests/groupby/test_groupby.py
+++ b/pandas/tests/groupby/test_groupby.py
@@ -2854,9 +2854,9 @@ def test_groupby_method_drop_na(method):
     df = DataFrame({"A": ["a", np.nan, "b", np.nan, "c"], "B": range(5)})
 
     if method == "nth":
-        result = df.groupby("A").agg(method, n=0)
+        result = getattr(df.groupby("A"), method)(n=0)
     else:
-        result = df.groupby("A").agg(method)
+        result = getattr(df.groupby("A"), method)()
 
     if method in ["first", "last"]:
         expected = DataFrame({"B": [0, 2, 4]}).set_index(