From 0f109d7db034c61e43d1aecb641578049a077d99 Mon Sep 17 00:00:00 2001
From: Charles Blackmon-Luca <20627856+charlesbluca@users.noreply.github.com>
Date: Mon, 9 Aug 2021 16:35:41 -0400
Subject: [PATCH] Apply series name to result of `SeriesGroupby.apply()`
 (#8939)

Closes #8899

Applies the name of `SeriesGroupby.obj` to the results of a `SeriesGroupby.apply()` operation; originally, this would be left as `None`.

Authors:
  - Charles Blackmon-Luca (https://github.com/charlesbluca)

Approvers:
  - Sheilah Kirui (https://github.com/skirui-source)
  - Michael Wang (https://github.com/isVoid)

URL: https://github.com/rapidsai/cudf/pull/8939
---
 python/cudf/cudf/core/groupby/groupby.py |  8 ++++++++
 python/cudf/cudf/tests/test_groupby.py   | 10 ++++++++++
 2 files changed, 18 insertions(+)

diff --git a/python/cudf/cudf/core/groupby/groupby.py b/python/cudf/cudf/core/groupby/groupby.py
index d51ae78e853..540fe665e33 100644
--- a/python/cudf/cudf/core/groupby/groupby.py
+++ b/python/cudf/cudf/core/groupby/groupby.py
@@ -1222,6 +1222,14 @@ def agg(self, func):
 
         return result
 
+    def apply(self, func):
+        result = super().apply(func)
+
+        # apply Series name to result
+        result.name = self.obj.name
+
+        return result
+
 
 class Grouper(object):
     def __init__(self, key=None, level=None):
diff --git a/python/cudf/cudf/tests/test_groupby.py b/python/cudf/cudf/tests/test_groupby.py
index fb8379315a9..e45963c1321 100644
--- a/python/cudf/cudf/tests/test_groupby.py
+++ b/python/cudf/cudf/tests/test_groupby.py
@@ -2104,3 +2104,13 @@ def test_groupby_first(data, agg):
     expect = pdf.groupby("a").agg(agg)
     got = gdf.groupby("a").agg(agg)
     assert_groupby_results_equal(expect, got, check_dtype=False)
+
+
+def test_groupby_apply_series_name():
+    def foo(x):
+        return x.sum()
+
+    got = make_frame(DataFrame, 3).groupby("x").y.apply(foo)
+    expect = make_frame(pd.DataFrame, 3).groupby("x").y.apply(foo)
+
+    assert expect.name == got.name