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BUG: read_csv not converting original col with keep_date_col true #44633

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Merged
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Nov 28, 2021
Merged

BUG: read_csv not converting original col with keep_date_col true #44633

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BUG: read_csv not converting original col with keep_date_col true
phofl Nov 26, 2021
3744193
Merge branch 'master' of https://github.com/pandas-dev/pandas into 13378
phofl Nov 26, 2021
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phofl Nov 28, 2021
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1 change: 1 addition & 0 deletions doc/source/whatsnew/v1.4.0.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -657,6 +657,7 @@ I/O
- Bug in :func:`read_csv` where reading multi-header input with unequal lengths incorrectly raising uncontrolled ``IndexError`` (:issue:`43102`)
- Bug in :func:`read_csv`, changed exception class when expecting a file path name or file-like object from ``OSError`` to ``TypeError`` (:issue:`43366`)
- Bug in :func:`read_csv` and :func:`read_fwf` ignoring all ``skiprows`` except first when ``nrows`` is specified for ``engine='python'`` (:issue:`44021`, :issue:`10261`)
- Bug in :func:`read_csv` keeping the original column in object format when ``keep_date_col=True`` is set (:issue:`13378`)
- Bug in :func:`read_json` not handling non-numpy dtypes correctly (especially ``category``) (:issue:`21892`, :issue:`33205`)
- Bug in :func:`json_normalize` where multi-character ``sep`` parameter is incorrectly prefixed to every key (:issue:`43831`)
- Bug in :func:`json_normalize` where reading data with missing multi-level metadata would not respect errors="ignore" (:issue:`44312`)
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6 changes: 6 additions & 0 deletions pandas/io/parsers/base_parser.py
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Expand Up @@ -1148,6 +1148,12 @@ def _isindex(colspec):
)

new_data[new_name] = col

# If original column can be converted to date we keep the converted values
# This can only happen if values are from single column
if len(colspec) == 1:
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this seems like very special casey here

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It is, yes. We can only keep the original column formatted as date, if it represents the whole date. In cases where two columns combined represent a date we can only keep the original format

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ok worth a comment about this then for future readers

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Done

new_data[colspec[0]] = col

new_cols.append(new_name)
date_cols.update(old_names)

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16 changes: 16 additions & 0 deletions pandas/tests/io/parser/test_parse_dates.py
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Expand Up @@ -1813,6 +1813,22 @@ def test_date_parser_usecols_thousands(all_parsers):
tm.assert_frame_equal(result, expected)


@skip_pyarrow
def test_parse_dates_and_keep_orgin_column(all_parsers):
# GH#13378
parser = all_parsers
data = """A
20150908
20150909
"""
result = parser.read_csv(
StringIO(data), parse_dates={"date": ["A"]}, keep_date_col=True
)
expected_data = [Timestamp("2015-09-08"), Timestamp("2015-09-09")]
expected = DataFrame({"date": expected_data, "A": expected_data})
tm.assert_frame_equal(result, expected)


def test_dayfirst_warnings():
# GH 12585
warning_msg_day_first = (
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