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BUG: merge with CategoricalIndex for left_on/right_on #48464

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Merged
merged 2 commits into from
Sep 9, 2022
Merged

BUG: merge with CategoricalIndex for left_on/right_on #48464

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9195563
BUG: merge with CategoricalIndex for left_on/right_on
jbrockmendel Sep 8, 2022
5cee3f5
GH refs
jbrockmendel Sep 8, 2022
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2 changes: 1 addition & 1 deletion doc/source/whatsnew/v1.6.0.rst
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Expand Up @@ -190,7 +190,7 @@ Groupby/resample/rolling

Reshaping
^^^^^^^^^
-
- Bug in :func:`join` when ``left_on`` or ``right_on`` is or includes a :class:`CategoricalIndex` incorrectly raising ``AttributeError`` (:issue:`48464`)
-

Sparse
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3 changes: 3 additions & 0 deletions pandas/core/reshape/merge.py
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Expand Up @@ -1250,6 +1250,9 @@ def _maybe_coerce_merge_keys(self) -> None:
if (len(lk) and not len(rk)) or (not len(lk) and len(rk)):
continue

lk = extract_array(lk, extract_numpy=True)
rk = extract_array(rk, extract_numpy=True)

lk_is_cat = is_categorical_dtype(lk.dtype)
rk_is_cat = is_categorical_dtype(rk.dtype)
lk_is_object = is_object_dtype(lk.dtype)
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12 changes: 12 additions & 0 deletions pandas/tests/reshape/merge/test_merge.py
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Expand Up @@ -2655,6 +2655,18 @@ def test_mergeerror_on_left_index_mismatched_dtypes():
merge(df_1, df_2, on=["C"], left_index=True)


def test_merge_on_left_categoricalindex():
# GH#48464 don't raise when left_on is a CategoricalIndex
ci = CategoricalIndex(range(3))

right = DataFrame({"A": ci, "B": range(3)})
left = DataFrame({"C": range(3, 6)})

res = merge(left, right, left_on=ci, right_on="A")
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Should the comment below the code change:

           # if either left or right is a categorical
            # then the must match exactly in categories & ordered

Apply here as well? Could you add a test where categories/ordered are different too?

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really shouldn't be relevant. its just a matter of CategoricalIndex vs Categorical

expected = merge(left, right, left_on=ci._data, right_on="A")
tm.assert_frame_equal(res, expected)


@pytest.mark.parametrize("dtype", [None, "Int64"])
def test_merge_outer_with_NaN(dtype):
# GH#43550
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