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ENH: Add force_suffixes boolean argument to pd.merge #61498

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ENH: Add force_suffixes boolean argument to pd.merge #61498

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c49ed5e
Add "force_suffixes" flag to pd.merge
kopytjuk May 26, 2025
8fa3cdb
Add a simple test for force-suffixes
kopytjuk May 26, 2025
d1c651d
Small refactor in merge tests
kopytjuk May 26, 2025
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2 changes: 2 additions & 0 deletions pandas/core/frame.py
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Original file line number Diff line number Diff line change
Expand Up @@ -11046,6 +11046,7 @@ def merge(
right_index: bool = False,
sort: bool = False,
suffixes: Suffixes = ("_x", "_y"),
force_suffixes: bool = False,
copy: bool | lib.NoDefault = lib.no_default,
indicator: str | bool = False,
validate: MergeValidate | None = None,
Expand All @@ -11065,6 +11066,7 @@ def merge(
right_index=right_index,
sort=sort,
suffixes=suffixes,
force_suffixes=force_suffixes,
indicator=indicator,
validate=validate,
)
Expand Down
17 changes: 14 additions & 3 deletions pandas/core/reshape/merge.py
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Original file line number Diff line number Diff line change
Expand Up @@ -153,6 +153,7 @@ def merge(
right_index: bool = False,
sort: bool = False,
suffixes: Suffixes = ("_x", "_y"),
force_suffixes: bool = False,
copy: bool | lib.NoDefault = lib.no_default,
indicator: str | bool = False,
validate: str | None = None,
Expand Down Expand Up @@ -395,6 +396,7 @@ def merge(
right_index=right_index,
sort=sort,
suffixes=suffixes,
force_suffixes=force_suffixes,
indicator=indicator,
validate=validate,
)
Expand All @@ -411,6 +413,7 @@ def _cross_merge(
right_index: bool = False,
sort: bool = False,
suffixes: Suffixes = ("_x", "_y"),
force_suffixes: bool = False,
indicator: str | bool = False,
validate: str | None = None,
) -> DataFrame:
Expand Down Expand Up @@ -447,6 +450,7 @@ def _cross_merge(
right_index=right_index,
sort=sort,
suffixes=suffixes,
force_suffixes=force_suffixes,
indicator=indicator,
validate=validate,
)
Expand Down Expand Up @@ -966,6 +970,7 @@ def __init__(
right_index: bool = False,
sort: bool = True,
suffixes: Suffixes = ("_x", "_y"),
force_suffixes: bool = False,
indicator: str | bool = False,
validate: str | None = None,
) -> None:
Expand All @@ -978,6 +983,8 @@ def __init__(
self.on = com.maybe_make_list(on)

self.suffixes = suffixes
self.force_suffixes = force_suffixes

self.sort = sort or how == "outer"

self.left_index = left_index
Expand Down Expand Up @@ -1088,7 +1095,7 @@ def _reindex_and_concat(
right = self.right[:]

llabels, rlabels = _items_overlap_with_suffix(
self.left._info_axis, self.right._info_axis, self.suffixes
self.left._info_axis, self.right._info_axis, self.suffixes, self.force_suffixes
)

if left_indexer is not None and not is_range_indexer(left_indexer, len(left)):
Expand Down Expand Up @@ -3007,7 +3014,7 @@ def _validate_operand(obj: DataFrame | Series) -> DataFrame:


def _items_overlap_with_suffix(
left: Index, right: Index, suffixes: Suffixes
left: Index, right: Index, suffixes: Suffixes, force_suffixes: bool = False
) -> tuple[Index, Index]:
"""
Suffixes type validation.
Expand All @@ -3023,7 +3030,11 @@ def _items_overlap_with_suffix(
"Provide 'suffixes' as a tuple instead."
)

to_rename = left.intersection(right)
if not force_suffixes:
to_rename = left.intersection(right)
else:
to_rename = left.union(right)

if len(to_rename) == 0:
return left, right

Expand Down
72 changes: 72 additions & 0 deletions pandas/tests/reshape/merge/test_merge.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2369,6 +2369,77 @@ def test_merge_suffix(col1, col2, kwargs, expected_cols):
tm.assert_frame_equal(result, expected)


@pytest.mark.parametrize("force_suffixes", [False, True])
def test_merge_suffix_with_force_simple(force_suffixes):
df1 = pd.DataFrame({
'ID': [1, 2, 3],
'Value': ['A', 'B', 'C']
})

df2 = pd.DataFrame({
'ID': [2, 3, 4],
'Value': ['D', 'E', 'F']
})

if force_suffixes:
expected = DataFrame([[2, 2, "B", "D"], [3, 3, "C", "E"]],
columns=["ID_left", "Value_left", "ID_right", "Value_right"])
else:
expected = DataFrame([[2, "B", "D"], [3, "C", "E"]],
columns=["ID", "Value_left", "Value_right"])

result = merge(df1, df2, on="ID", suffixes=("_left", "_right"),
force_suffixes=force_suffixes)
tm.assert_frame_equal(result, expected)

@pytest.mark.parametrize("force_suffixes", [False, True])
def test_merge_suffix_with_force_multi_column(force_suffixes):
a = DataFrame({"A": [1, 2, 3, 98], "B": [4, 5, 6, 99], "ALPHABET": ["A", "B", "C", "Z"]})
b = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "alphabet": ["a", "b", "c"]})

if force_suffixes:
expected = DataFrame([[1, 4, "A", 1, 4, "a"], [2, 5, "B", 2, 5, "b"], [3, 6, "C", 3, 6, "c"]],
columns=["A_x", "B_x", "ALPHABET_x", "a_y", "b_y", "alphabet_y"])
else:
expected = DataFrame([[1, 4, "A", 1, 4, "a"], [2, 5, "B", 2, 5, "b"], [3, 6, "C", 3, 6, "c"]],
columns=["A", "B", "ALPHABET", "a", "b", "alphabet"])

result = merge(a, b, left_on=["A", "B"], right_on=["a", "b"],
force_suffixes=force_suffixes)
tm.assert_frame_equal(result, expected)

@pytest.mark.parametrize(
"col1, col2, kwargs, expected_cols",
[
(0, 0, {"suffixes": ("", "_dup")}, ["0", "0_dup"]),
(0, 0, {"suffixes": (None, "_dup")}, [0, "0_dup"]),
(0, 0, {"suffixes": ("_x", "_y")}, ["0_x", "0_y"]),
(0, 0, {"suffixes": ["_x", "_y"]}, ["0_x", "0_y"]),
("a", 0, {"suffixes": (None, "_y")}, ["a", "0_y"]),
(0.0, 0.0, {"suffixes": ("_x", None)}, ["0.0_x", 0.0]),
("b", "b", {"suffixes": (None, "_y")}, ["b", "b_y"]),
("a", "a", {"suffixes": ("_x", None)}, ["a_x", "a"]),
("a", "b", {"suffixes": ("_x", None)}, ["a_x", "b"]),
("a", "a", {"suffixes": (None, "_x")}, ["a", "a_x"]),
(0, 0, {"suffixes": ("_a", None)}, ["0_a", 0]),
("a", "a", {}, ["a_x", "a_y"]),
(0, 0, {}, ["0_x", "0_y"]),
],
)
def test_merge_suffix_with_force(col1, col2, kwargs, expected_cols):
# issue: 24782
a = DataFrame({col1: [1, 2, 3]})
b = DataFrame({col2: [4, 5, 6]})

expected = DataFrame([[1, 4], [2, 5], [3, 6]], columns=expected_cols)

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

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


@pytest.mark.parametrize(
"how,expected",
[
Expand Down Expand Up @@ -2577,6 +2648,7 @@ def test_categorical_non_unique_monotonic(n_categories):
tm.assert_frame_equal(expected, result)



def test_merge_join_categorical_multiindex():
# From issue 16627
a = {
Expand Down
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