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DEPR: Disallow dtype inference when setting Index into DataFrame #56102

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Merged
merged 3 commits into from
Dec 9, 2023
Merged

DEPR: Disallow dtype inference when setting Index into DataFrame #56102

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ca5f53f
DEPR: Disallow dtype inference when setting Index into DataFrame
phofl Nov 21, 2023
bce2db5
Merge branch 'main' into deprecate_setitem_coercing
phofl Nov 29, 2023
3aa4cc7
Merge branch 'main' into deprecate_setitem_coercing
phofl Dec 8, 2023
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1 change: 1 addition & 0 deletions doc/source/whatsnew/v2.2.0.rst
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Expand Up @@ -455,6 +455,7 @@ Other Deprecations
- Deprecated allowing non-keyword arguments in :meth:`DataFrame.to_xml` except ``path_or_buffer``. (:issue:`54229`)
- Deprecated allowing passing :class:`BlockManager` objects to :class:`DataFrame` or :class:`SingleBlockManager` objects to :class:`Series` (:issue:`52419`)
- Deprecated downcasting behavior in :meth:`Series.where`, :meth:`DataFrame.where`, :meth:`Series.mask`, :meth:`DataFrame.mask`, :meth:`Series.clip`, :meth:`DataFrame.clip`; in a future version these will not infer object-dtype columns to non-object dtype, or all-round floats to integer dtype. Call ``result.infer_objects(copy=False)`` on the result for object inference, or explicitly cast floats to ints. To opt in to the future version, use ``pd.set_option("future.no_silent_downcasting", True)`` (:issue:`53656`)
- Deprecated dtype inference when setting a :class:`Index` into a :class:`DataFrame`, cast explicitly instead (:issue:`56102`)
- Deprecated including the groups in computations when using :meth:`.DataFrameGroupBy.apply` and :meth:`.DataFrameGroupBy.resample`; pass ``include_groups=False`` to exclude the groups (:issue:`7155`)
- Deprecated indexing an :class:`Index` with a boolean indexer of length zero (:issue:`55820`)
- Deprecated not passing a tuple to :class:`.DataFrameGroupBy.get_group` or :class:`.SeriesGroupBy.get_group` when grouping by a length-1 list-like (:issue:`25971`)
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16 changes: 15 additions & 1 deletion pandas/core/frame.py
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Expand Up @@ -5219,7 +5219,21 @@ def _sanitize_column(self, value) -> tuple[ArrayLike, BlockValuesRefs | None]:

if is_list_like(value):
com.require_length_match(value, self.index)
return sanitize_array(value, self.index, copy=True, allow_2d=True), None
arr = sanitize_array(value, self.index, copy=True, allow_2d=True)
if (
isinstance(value, Index)
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might be more performant to do the Index check before the sanitize_array?

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Why? We have to sanitise anyway?

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if you know you have an Index (and no dtype), sanitize_array boils down to:

if len(value) != len(index): raise ...
return value._values

so a lot of sanitize_array may be made unnecessary in this case

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That's what I want in the future, but we go through maybe_infer_to_datetimelike at the moment which changes the dtype, so we can't shortcut this before we enforce the deprecation

and value.dtype == "object"
and arr.dtype != value.dtype
): #
# TODO: Remove kludge in sanitize_array for string mode when enforcing
# this deprecation
warnings.warn(
"Setting an Index with object dtype into a DataFrame will no longer "
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is "will no longer" clear enough that this refers to a future version/deprecation?

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good point, I'll put up a PR to clarify

"infer another dtype. Cast the Index explicitly before setting.",
FutureWarning,
stacklevel=find_stack_level(),
)
return arr, None

@property
def _series(self):
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18 changes: 18 additions & 0 deletions pandas/tests/frame/indexing/test_setitem.py
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Expand Up @@ -786,6 +786,24 @@ def test_loc_setitem_ea_dtype(self):
df.iloc[:, 0] = Series([11], dtype="Int64")
tm.assert_frame_equal(df, expected)

def test_setitem_object_inferring(self):
# GH#56102
idx = Index([Timestamp("2019-12-31")], dtype=object)
df = DataFrame({"a": [1]})
with tm.assert_produces_warning(FutureWarning, match="infer"):
df.loc[:, "b"] = idx
with tm.assert_produces_warning(FutureWarning, match="infer"):
df["c"] = idx

expected = DataFrame(
{
"a": [1],
"b": Series([Timestamp("2019-12-31")], dtype="datetime64[ns]"),
"c": Series([Timestamp("2019-12-31")], dtype="datetime64[ns]"),
}
)
tm.assert_frame_equal(df, expected)


class TestSetitemTZAwareValues:
@pytest.fixture
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