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BUG: Preserve column names in DataFrame.from_records when nrows=0 #61143

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BUG: Preserve column names in DataFrame.from_records when nrows=0 #61143

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5dd7786
Fix from records() to preserve columns when nrows=0
kpvenkat47 Mar 18, 2025
cc21929
Update empty DataFrame initialization to preserve columns - Changed '…
kpvenkat47 Mar 18, 2025
e2fbceb
Updated PR #6114 based on review feedback
kpvenkat47 Mar 26, 2025
81ad960
Merge branch 'kpvenkat47-fix-from-records-nrows' into fix-empty-df-co…
kpvenkat47 Mar 26, 2025
5dcc1ac
All reviews are updated.Please check
kpvenkat47 Apr 1, 2025
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2 changes: 1 addition & 1 deletion pandas/core/frame.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2231,7 +2231,7 @@ def maybe_reorder(

if is_iterator(data):
if nrows == 0:
return cls()
return cls(columns=columns)

try:
first_row = next(data)
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7 changes: 7 additions & 0 deletions pandas/core/frame_test_constructors.py
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@@ -0,0 +1,7 @@
import pandas as pd
def test_empty_df_preserve_col():
rows = []
df = pd.DataFrame.from_records(iter(rows), columns=['col_1', 'Col_2'], nrows=0)
assert list(df.columns)==['col_1', 'Col_2']
assert len(df) == 0
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Can you follow the dev docs here: https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests

Namely, search the current tests for from_records and that should give a good indication of where to place this test.

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This file needs to be removed.


6 changes: 6 additions & 0 deletions pandas/tests/frame/test_constructors.py
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Expand Up @@ -2780,6 +2780,12 @@ def test_construction_nan_value_timedelta64_dtype(self):
)
tm.assert_frame_equal(result, expected)

def test_from_records_empty_iterator_with_preserve_columns(self):
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Can you move this test to tests/frame/constructors/test_from_records.py


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Can you start the test with a comment referencing the issue. # GH#61140

rows = []
df = pd.DataFrame.from_records(iter(rows), columns=["col_1", "Col_2"], nrows=0)
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Can you call the result result instead of df.

assert list(df.columns) == ["col_1", "Col_2"]
assert len(df) == 0
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Instead of these two lines, can you check the entire result.

expected = DataFrame(...)
tm.assert_frame_equal(result, expected)`


class TestDataFrameConstructorIndexInference:
def test_frame_from_dict_of_series_overlapping_monthly_period_indexes(self):
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