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Fix DataFrame.agg produces different types if the DataFrame is empty #41722

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Fix DataFrame.agg produces different types if the DataFrame is empty #41722

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7e5eb1b
resolve different types if the DataFrame is empty
May 29, 2021
878c33b
remove unnecessary import
May 29, 2021
3e8b8d3
resolve quotes
May 29, 2021
e130bd5
add comma
May 29, 2021
f94905b
standardize the test
May 30, 2021
d5fad83
resolve line spacing
May 30, 2021
190e8bf
autopep
May 30, 2021
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3 changes: 3 additions & 0 deletions pandas/core/frame.py
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Original file line number Diff line number Diff line change
Expand Up @@ -8534,6 +8534,9 @@ def aggregate(self, func=None, axis: Axis = 0, *args, **kwargs):
result_in_dict = relabel_result(result, func, columns, order)
result = DataFrame(result_in_dict, index=columns)

if isinstance(result, DataFrame):
result = result.squeeze()

return result

agg = aggregate
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21 changes: 21 additions & 0 deletions pandas/tests/frame/test_aggregate.py
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@@ -0,0 +1,21 @@
import numpy as np

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these go in pandas/tests/apply/test_frame_apply.py

there are already extensive tests, so find a good place to exercise the empty case

we have these, so model after

(pandas) jreback@lhs2:~/pandas-dev$ grep -r empty pandas/tests/apply/|grep def
pandas/tests/apply/test_frame_transform.py:def test_transform_empty_listlike(float_frame, ops, frame_or_series):
pandas/tests/apply/test_frame_transform.py:def test_transform_empty_dictlike(float_frame, ops, frame_or_series):
pandas/tests/apply/test_frame_transform.py:def test_transform_empty_dataframe():
pandas/tests/apply/test_series_apply.py:def test_apply_empty_integer_series_with_datetime_index():
pandas/tests/apply/test_series_apply.py:def test_map_empty(index):
pandas/tests/apply/test_frame_apply.py:def test_apply_empty(float_frame):
pandas/tests/apply/test_frame_apply.py:def test_apply_with_reduce_empty():
pandas/tests/apply/test_frame_apply.py:def test_apply_funcs_over_empty(func):
pandas/tests/apply/test_frame_apply.py:def test_nunique_empty():
pandas/tests/apply/test_frame_apply.py:def test_apply_empty_infer_type():
pandas/tests/apply/test_frame_apply.py:def test_apply_empty_list_reduce():

import pandas as pd

from pandas import (
DataFrame,
Series,
)

import pandas._testing as tm


def _check_mixed_int(df, dtype=None):
# GH#41672
result = DataFrame([], columns=["lang", "name"])
result = result.agg({"name": lambda y: y.values})
assert type(result) == Series

result = DataFrame([["a", "boof"]], columns=["lang", "name"])
result = result.agg({"name": lambda y: y.values})
assert type(result) == Series