BUG: Preserve column names in DataFrame.from_records when nrows=0 #61143
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…if nrows == 0' to return Cls(columns=columns) in core/frame.py. - Added test to verify column preservation.
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Thanks for the PR! When making a PR, follow these steps here:
https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#making-a-pull-request
namely step 4.
| 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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rhshadrach
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I have updated the PR with the latest changes based on feedback. Please review again. |
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Looks good! The change in One minor point: It looks like the test was also added as a new standalone file |
| @@ -2780,6 +2780,12 @@ def test_construction_nan_value_timedelta64_dtype(self): | |||
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| tm.assert_frame_equal(result, expected) | |||
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| def test_from_records_empty_iterator_with_preserve_columns(self): | |||
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Can you start the test with a comment referencing the issue. # GH#61140
| 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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| @@ -2780,6 +2780,12 @@ def test_construction_nan_value_timedelta64_dtype(self): | |||
| ) | |||
| tm.assert_frame_equal(result, expected) | |||
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| 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
| def test_from_records_empty_iterator_with_preserve_columns(self): | ||
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| 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)`
rhshadrach
changed the title
Description
Updates pandas/core/frame.py to preserve column names in empty DataFrames when nrows == 0. Changed from return Cls() to return Cls(columns=columns).
Closes #61140
Changes Made
Testing