From cec322a95fd44eaf5f520774c80952910343727e Mon Sep 17 00:00:00 2001 From: Marco Neumann Date: Thu, 17 Oct 2019 15:17:24 +0200 Subject: [PATCH] TST: add regression test for all-none-groupby Closes #21624 --- pandas/tests/groupby/test_groupby.py | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/pandas/tests/groupby/test_groupby.py b/pandas/tests/groupby/test_groupby.py index 6212a37472000..dff5baa9b5984 100644 --- a/pandas/tests/groupby/test_groupby.py +++ b/pandas/tests/groupby/test_groupby.py @@ -1944,3 +1944,13 @@ def test_shift_bfill_ffill_tz(tz_naive_fixture, op, expected): result = getattr(grouped, op)() expected = DataFrame(expected).assign(time=lambda x: x.time.dt.tz_localize(tz)) assert_frame_equal(result, expected) + + +def test_groupby_only_none_group(): + # see GH21624 + # this was crashing with "ValueError: Length of passed values is 1, index implies 0" + df = pd.DataFrame({"g": [None], "x": 1}) + actual = df.groupby("g")["x"].transform("sum") + expected = pd.Series([np.nan], name="x") + + assert_series_equal(actual, expected)