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ENH: accept None behaviour for suffixes in DataFrame.merge #25243

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ENH: accept None behaviour for suffixes in DataFrame.merge #25243

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1 change: 1 addition & 0 deletions doc/source/whatsnew/v0.25.0.rst
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Expand Up @@ -21,6 +21,7 @@ Other Enhancements

- Indexing of ``DataFrame`` and ``Series`` now accepts zerodim ``np.ndarray`` (:issue:`24919`)
- :meth:`Timestamp.replace` now supports the ``fold`` argument to disambiguate DST transition times (:issue:`25017`)
- :function:`pandas.merge` now accepts ``None`` as input of suffixes (:issue:`25242`)
- :meth:`DataFrame.at_time` and :meth:`Series.at_time` now support :meth:`datetime.time` objects with timezones (:issue:`24043`)
- ``Series.str`` has gained :meth:`Series.str.casefold` method to removes all case distinctions present in a string (:issue:`25405`)
- :meth:`DataFrame.set_index` now works for instances of ``abc.Iterator``, provided their output is of the same length as the calling frame (:issue:`22484`, :issue:`24984`)
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8 changes: 0 additions & 8 deletions pandas/core/frame.py
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Expand Up @@ -273,14 +273,6 @@
4 bar 2 bar 6
5 baz 3 baz 7

Merge DataFrames df1 and df2, but raise an exception if the DataFrames have
any overlapping columns.

>>> df1.merge(df2, left_on='lkey', right_on='rkey', suffixes=(False, False))
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did we previously accept False here? or was this added in the previous PR?

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this was not added in previous PR.
IIUC previously the code was something like
if not lsuffix and not rsuffix, so False and None are both not allowed, and will raise the ValueError,
but since in this PR, we don't raise error or warnings when there are duplicate column names, so i removed this part of docstring. @jreback @jorisvandenbossche

Traceback (most recent call last):
...
ValueError: columns overlap but no suffix specified:
Index(['value'], dtype='object')
"""

# -----------------------------------------------------------------------
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3 changes: 0 additions & 3 deletions pandas/core/internals/managers.py
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Expand Up @@ -1963,9 +1963,6 @@ def items_overlap_with_suffix(left, lsuffix, right, rsuffix):
if len(to_rename) == 0:
return left, right
else:
if not lsuffix and not rsuffix:
raise ValueError('columns overlap but no suffix specified: '
'{rename}'.format(rename=to_rename))

def renamer(x, suffix):
"""Rename the left and right indices.
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8 changes: 5 additions & 3 deletions pandas/core/reshape/merge.py
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Expand Up @@ -159,13 +159,13 @@ def merge_ordered(left, right, on=None,
left DataFrame
fill_method : {'ffill', None}, default None
Interpolation method for data
suffixes : Sequence, default is ("_x", "_y")
suffixes : Sequence or None, default is ("_x", "_y")
A length-2 sequence where each element is optionally a string
indicating the suffix to add to overlapping column names in
`left` and `right` respectively. Pass a value of `None` instead
of a string to indicate that the column name from `left` or
`right` should be left as-is, with no suffix. At least one of the
values must not be None.
`right` should be left as-is, with no suffix. `None` means
keep both name of overlapping columns as-is.
.. versionchanged:: 0.25.0
how : {'left', 'right', 'outer', 'inner'}, default 'outer'
Expand Down Expand Up @@ -495,6 +495,8 @@ def __init__(self, left, right, how='inner', on=None,

self.copy = copy
self.suffixes = suffixes
if self.suffixes is None:
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you can change the signature I think to suffixes=None

self.suffixes = (None, None)
self.sort = sort

self.left_index = left_index
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6 changes: 0 additions & 6 deletions pandas/tests/frame/test_join.py
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Expand Up @@ -97,12 +97,6 @@ def test_join_index(frame):
with pytest.raises(ValueError, match='join method'):
f.join(f2, how='foo')

# corner case - overlapping columns
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hmm, this used to error. I am not sure I like this change. cc @jorisvandenbossche

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yes, this removal is made because in last PR we found out pandas don't explicitly refuse overlapping columns, e.g.

df1 = pd.DataFrame({"a": [1, 2], "b": [3, 4], "b_x": [5, 6]})
df2 = pd.DataFrame({"a": [1, 2], "b": [4, 5]})
df1.merge(df2, on="a")

the output will still contain two "b_x" columns. @jorisvandenbossche @simonjayhawkins

msg = 'columns overlap but no suffix'
for how in ('outer', 'left', 'inner'):
with pytest.raises(ValueError, match=msg):
frame.join(frame, how=how)


def test_join_index_more(frame):
af = frame.loc[:, ['A', 'B']]
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46 changes: 12 additions & 34 deletions pandas/tests/reshape/merge/test_merge.py
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Expand Up @@ -1618,7 +1618,18 @@ def test_merge_series(on, left_on, right_on, left_index, right_index, nm):
("a", "a", dict(suffixes=[None, "_x"]), ["a", "a_x"]),
(0, 0, dict(suffixes=["_a", None]), ["0_a", 0]),
("a", "a", dict(), ["a_x", "a_y"]),
(0, 0, dict(), ["0_x", "0_y"])
(0, 0, dict(), ["0_x", "0_y"]),
# accept 2-length None alike suffixes input
(0, 0, dict(suffixes=[None, None]), [0, 0]),
(0, 0, dict(suffixes=(None, '')), [0, '0']),
(0, 0, dict(suffixes=['', '']), ['0', '0']),
("a", "a", dict(suffixes=[None, None]), ["a", "a"]),
("a", "a", dict(suffixes=["", None]), ["a", "a"]),
("a", "a", dict(suffixes=(None, None)), ["a", "a"]),
("a", "a", dict(suffixes=('', '')), ["a", "a"]),
# accept None as suffixes
(0, 0, dict(suffixes=None), [0, 0]),
("a", "a", dict(suffixes=None), ["a", "a"])
])
def test_merge_suffix(col1, col2, kwargs, expected_cols):
# issue: 24782
Expand All @@ -1633,36 +1644,3 @@ def test_merge_suffix(col1, col2, kwargs, expected_cols):

result = pd.merge(a, b, left_index=True, right_index=True, **kwargs)
tm.assert_frame_equal(result, expected)


@pytest.mark.parametrize("col1, col2, suffixes", [
("a", "a", [None, None]),
("a", "a", (None, None)),
("a", "a", ("", None)),
(0, 0, [None, None]),
(0, 0, (None, ""))
])
def test_merge_suffix_error(col1, col2, suffixes):
# issue: 24782
a = pd.DataFrame({col1: [1, 2, 3]})
b = pd.DataFrame({col2: [3, 4, 5]})

# TODO: might reconsider current raise behaviour, see issue 24782
msg = "columns overlap but no suffix specified"
with pytest.raises(ValueError, match=msg):
pd.merge(a, b, left_index=True, right_index=True, suffixes=suffixes)


@pytest.mark.parametrize("col1, col2, suffixes", [
("a", "a", None),
(0, 0, None)
])
def test_merge_suffix_none_error(col1, col2, suffixes):
# issue: 24782
a = pd.DataFrame({col1: [1, 2, 3]})
b = pd.DataFrame({col2: [3, 4, 5]})

# TODO: might reconsider current raise behaviour, see GH24782
msg = "iterable"
with pytest.raises(TypeError, match=msg):
pd.merge(a, b, left_index=True, right_index=True, suffixes=suffixes)
6 changes: 0 additions & 6 deletions pandas/tests/reshape/merge/test_multi.py
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Expand Up @@ -508,12 +508,6 @@ def test_join_multi_levels(self):
with pytest.raises(ValueError):
household.join(portfolio, how='inner')

portfolio2 = portfolio.copy()
portfolio2.index.set_names(['household_id', 'foo'])

with pytest.raises(ValueError):
portfolio2.join(portfolio, how='inner')

def test_join_multi_levels2(self):

# some more advanced merges
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