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ENH: concat of nullable int + bool preserves int dtype #34985

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Jul 8, 2020
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ENH: concat of nullable int + bool preserves int dtype #34985

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374a90b
ENH: concat of nullable int + bool preserves int dtype
jorisvandenbossche Jun 25, 2020
fd15be2
add issue number to whatsnew
jorisvandenbossche Jun 25, 2020
8b18538
Merge remote-tracking branch 'upstream/master' into concat-int
jorisvandenbossche Jul 3, 2020
bb7aa27
Merge remote-tracking branch 'upstream/master' into concat-int
TomAugspurger Jul 7, 2020
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2 changes: 1 addition & 1 deletion doc/source/whatsnew/v1.1.0.rst
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Expand Up @@ -311,7 +311,7 @@ Other enhancements
- :meth:`DataFrame.hist`, :meth:`Series.hist`, :meth:`core.groupby.DataFrameGroupBy.hist`, and :meth:`core.groupby.SeriesGroupBy.hist` have gained the ``legend`` argument. Set to True to show a legend in the histogram. (:issue:`6279`)
- :func:`concat` and :meth:`~DataFrame.append` now preserve extension dtypes, for example
combining a nullable integer column with a numpy integer column will no longer
result in object dtype but preserve the integer dtype (:issue:`33607`, :issue:`34339`).
result in object dtype but preserve the integer dtype (:issue:`33607`, :issue:`34339`, :issue:`34095`).
- :meth:`~pandas.io.gbq.read_gbq` now allows to disable progress bar (:issue:`33360`).
- :meth:`~pandas.io.gbq.read_gbq` now supports the ``max_results`` kwarg from ``pandas-gbq`` (:issue:`34639`).
- :meth:`Dataframe.cov` and :meth:`Series.cov` now support a new parameter ddof to support delta degrees of freedom as in the corresponding numpy methods (:issue:`34611`).
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9 changes: 6 additions & 3 deletions pandas/core/arrays/integer.py
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Expand Up @@ -92,10 +92,13 @@ def construct_array_type(cls) -> Type["IntegerArray"]:
return IntegerArray

def _get_common_dtype(self, dtypes: List[DtypeObj]) -> Optional[DtypeObj]:
# for now only handle other integer types
# we only handle nullable EA dtypes and numeric numpy dtypes
if not all(
isinstance(t, _IntegerDtype)
or (isinstance(t, np.dtype) and np.issubdtype(t, np.integer))
isinstance(t, BaseMaskedDtype)
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I worry a bit about this. I could easily see other arrays using the BaseMasked stuff (e.g. StringArray) that shouldn't necessarily be considered "integer-like" for this concat.

So I'd be more comfortable with (_IntegerDtype, BooleanDtype) even though those are synonymous today.

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agree with @TomAugspurger here

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@jorisvandenbossche jorisvandenbossche Jun 25, 2020 •
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The check for BaseMaskedDtype ensures the dtype has a numpy_dtype, and below we still do a np.find_common_type on the result. So assuming you have int + string, numpy will return object dtype for that, in which case we still return None from this function (which is equivalent as making the check here more strict and returning None here).

So even when we make StringArray a masked array, this method should already work as expected.

And doing it this way, I don't have to add FloatingDtype to the list of (_IntegerDtype, BooleanDtype) in the floating PR.

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@TomAugspurger TomAugspurger Jun 25, 2020 •
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So even when we make StringArray a masked array, this method should already work as expected.

Good to know.

I don't have to add FloatingDtype to the list of (_IntegerDtype, BooleanDtype) in the floating PR.

Will we want to return None here for float? Or I suppose the find_common_type stuff will handle that as well, just like string?

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@jreback does #34985 (comment) make sense?

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make sense, though still feel that there is no downside to being explict about listing the 2 dtypes directy; its more obvious. Agreed that if in the future we add more convertable to integer dtypes they won't automatically be added, but i think that is of lesser benefit that better readability here (i mean you could add a comment, but i think listing the classes is better)

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I think how it is written now also gives a good message: all BaseMaskedDtype subclasses are supported by this method (which is the case, even though some might return None from the function later on)

Will we want to return None here for float? Or I suppose the find_common_type stuff will handle that as well, just like string?

Yes, right now we would still return None for float (only if the common numpy dtype is an integer dtype, an EA dtype is returned). Once we have FloatingArray, we would add an additional check for the case that the common numpy dtype is a float dtype, and then return an EA floating dtype.

or (
isinstance(t, np.dtype)
and (np.issubdtype(t, np.number) or np.issubdtype(t, np.bool_))
)
for t in dtypes
):
return None
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45 changes: 43 additions & 2 deletions pandas/tests/arrays/integer/test_concat.py
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@@ -1,3 +1,4 @@
import numpy as np
import pytest

import pandas as pd
Expand All @@ -15,12 +16,52 @@
(["Int32", "UInt32"], "Int64"),
# this still gives object (awaiting float extension dtype)
(["Int64", "UInt64"], "object"),
(["Int64", "boolean"], "Int64"),
(["UInt8", "boolean"], "UInt8"),
],
)
def test_concat_series(to_concat_dtypes, result_dtype):

result = pd.concat([pd.Series([1, 2, pd.NA], dtype=t) for t in to_concat_dtypes])
expected = pd.concat([pd.Series([1, 2, pd.NA], dtype=object)] * 2).astype(
result = pd.concat([pd.Series([0, 1, pd.NA], dtype=t) for t in to_concat_dtypes])
expected = pd.concat([pd.Series([0, 1, pd.NA], dtype=object)] * 2).astype(
result_dtype
)
tm.assert_series_equal(result, expected)

# order doesn't matter for result
result = pd.concat(
[pd.Series([0, 1, pd.NA], dtype=t) for t in to_concat_dtypes[::-1]]
)
expected = pd.concat([pd.Series([0, 1, pd.NA], dtype=object)] * 2).astype(
result_dtype
)
tm.assert_series_equal(result, expected)


@pytest.mark.parametrize(
"to_concat_dtypes, result_dtype",
[
(["Int64", "int64"], "Int64"),
(["UInt64", "uint64"], "UInt64"),
(["Int8", "int8"], "Int8"),
(["Int8", "int16"], "Int16"),
(["UInt8", "int8"], "Int16"),
(["Int32", "uint32"], "Int64"),
# this still gives object (awaiting float extension dtype)
(["Int64", "uint64"], "object"),
(["Int64", "bool"], "Int64"),
(["UInt8", "bool"], "UInt8"),
],
)
def test_concat_series_with_numpy(to_concat_dtypes, result_dtype):

s1 = pd.Series([0, 1, pd.NA], dtype=to_concat_dtypes[0])
s2 = pd.Series(np.array([0, 1], dtype=to_concat_dtypes[1]))
result = pd.concat([s1, s2], ignore_index=True)
expected = pd.Series([0, 1, pd.NA, 0, 1], dtype=object).astype(result_dtype)
tm.assert_series_equal(result, expected)

# order doesn't matter for result
result = pd.concat([s2, s1], ignore_index=True)
expected = pd.Series([0, 1, 0, 1, pd.NA], dtype=object).astype(result_dtype)
tm.assert_series_equal(result, expected)