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BUG: inconsistent behaviour for empty DataFrames #48327

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BUG: inconsistent behaviour for empty DataFrames #48327

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c4e83b2
add test for inconsistent dataframe representation for empty inputs
ntachukwu Aug 31, 2022
399e209
precomit
ntachukwu Aug 31, 2022
0d7223a
add test for empty df constructs
ntachukwu Sep 6, 2022
8f7bc39
precommit
ntachukwu Sep 6, 2022
ea79bd9
add test for empty df without column name
ntachukwu Sep 6, 2022
5c945d5
add test for groupby sample on empty inputs
ntachukwu Sep 8, 2022
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15 changes: 15 additions & 0 deletions pandas/tests/groupby/test_apply.py
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Original file line number Diff line number Diff line change
@@ -1,3 +1,4 @@
import datetime as dt
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The datetime module is already imported below as well (so you can update your code to use the existing import)

from datetime import (
date,
datetime,
Expand Down Expand Up @@ -1331,3 +1332,17 @@ def test_result_name_when_one_group(name):
expected = Series([1, 2], name=name)

tm.assert_series_equal(result, expected)


def test_empty_inputs_with_apply_inconsistency():
df = pd.DataFrame([(dt.date.today(), 2, 3)], columns=["date", "a", "b"])
df["date"] = pd.to_datetime(df["date"])
df = df[df["b"] == 1] # An empty dataframe
result = df.set_index("date").groupby("a", group_keys=True).apply(lambda x: x)

df2 = pd.DataFrame([(dt.date.today(), 2, 3)], columns=["date", "a", "b"])
df2["date"] = pd.to_datetime(df2["date"])
df3 = df2.set_index("date").groupby("a", group_keys=True).apply(lambda x: x)
expected = df3.iloc[:0] # An empty dataframe

tm.assert_equal(result, expected)
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Suggested change
tm.assert_equal(result, expected)
tm.assert_frame_equal(result, expected)