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BUG: fix groupby.quantile inconsistency when interpolation='nearest' #56926

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Merged
merged 4 commits into from
Jan 18, 2024
Merged

BUG: fix groupby.quantile inconsistency when interpolation='nearest' #56926

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23a149c
BUG: fix groupby.quantile inconsistency when interpolation='nearest'
yuanx749 Jan 17, 2024
44747c3
add whatsnew
yuanx749 Jan 17, 2024
b420554
Merge remote-tracking branch 'upstream/main' into groupby.quantile
yuanx749 Jan 18, 2024
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yuanx749 Jan 18, 2024
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2 changes: 1 addition & 1 deletion doc/source/whatsnew/v2.3.0.rst
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Expand Up @@ -187,7 +187,7 @@ Plotting

Groupby/resample/rolling
^^^^^^^^^^^^^^^^^^^^^^^^
-
- Bug in :meth:`.DataFrameGroupBy.quantile` when ``interpolation="nearest"`` is inconsistent with :meth:`DataFrame.quantile` (:issue:`47942`)
-

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2 changes: 1 addition & 1 deletion pandas/_libs/groupby.pyx
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Expand Up @@ -1286,7 +1286,7 @@ def group_quantile(
elif interp == INTERPOLATION_MIDPOINT:
out[i, k] = (val + next_val) / 2.0
elif interp == INTERPOLATION_NEAREST:
if frac > .5 or (frac == .5 and q_val > .5): # Always OK?
if frac > .5 or (frac == .5 and idx % 2 == 1): # Always OK?
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Could you replace # Always OK? with a short comment above what idx % 2 == 1 is for?

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I added a comment.

out[i, k] = next_val
else:
out[i, k] = val
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14 changes: 1 addition & 13 deletions pandas/tests/groupby/methods/test_quantile.py
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Expand Up @@ -38,19 +38,7 @@
],
)
@pytest.mark.parametrize("q", [0, 0.25, 0.5, 0.75, 1])
def test_quantile(interpolation, a_vals, b_vals, q, request):
if (
interpolation == "nearest"
and q == 0.5
and isinstance(b_vals, list)
and b_vals == [4, 3, 2, 1]
):
request.applymarker(
pytest.mark.xfail(
reason="Unclear numpy expectation for nearest "
"result with equidistant data"
)
)
def test_quantile(interpolation, a_vals, b_vals, q):
all_vals = pd.concat([pd.Series(a_vals), pd.Series(b_vals)])

a_expected = pd.Series(a_vals).quantile(q, interpolation=interpolation)
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