8000 DOC: Add clarifications np.argpartition by JuliaPoo · Pull Request #26716 · numpy/numpy · GitHub
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DOC: Add clarifications np.argpartition #26716

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merged 4 commits into from
Jul 1, 2024
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DOC: Add clarifications np.argpartition #26716

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72b943c
DOC: Add clarifications np.argpartition
JuliaPoo Jun 17, 2024
2398d9c
DOC+TST: Specify np.nan sort order in partition functions
JuliaPoo Jun 28, 2024
05a3b82
Update numpy/_core/tests/test_multiarray.py
JuliaPoo Jul 1, 2024
456c4a9
DOC: Clean docs for argpartition
JuliaPoo Jul 1, 2024
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DOC+TST: Specify np.nan sort order in partition functions
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JuliaPoo committed Jun 28, 2024
commit 2398d9cbc4210b20666c2469d1b1cc94bcbad2d3
4 changes: 3 additions & 1 deletion numpy/_core/fromnumeric.py
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Expand Up @@ -823,6 +823,8 @@ def partition(a, kth, axis=-1, kind='introselect', order=None):
the real parts except when they are equal, in which case the order
is determined by the imaginary parts.

The sort order of ``np.nan`` is bigger than ``np.inf``.

Examples
--------
>>> a = np.array([7, 1, 7, 7, 1, 5, 7, 2, 3, 2, 6, 2, 3, 0])
Expand Down Expand Up @@ -923,7 +925,7 @@ def argpartition(a, kth, axis=-1, kind='introselect', order=None):
is unstable, and hence the returned indices are not guaranteed
to be the earliest/latest occurrence of the element.

The treatment of ``np.nan`` in the input array is undefined.
The sort order of ``np.nan`` is bigger than ``np.inf``.

See `partition` for notes on the different selection algorithms.
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I don't understand this comment. Aren't we in the partition function docstring? Does this docstring show up in a different function as well?

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@JuliaPoo JuliaPoo Jul 1, 2024 •
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The sort order is defined in the docstring for np.sort, but since np.partition uses a different implementation, I thought it would be helpful to also define the sort order of np.partition.

I've removed notes regarding the sort order from np.argpartition and instead linked it to the docs for np.partition in the latest commit, this follows what np.sort and np.argsort did.


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10 changes: 10 additions & 0 deletions numpy/_core/tests/test_multiarray.py
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Expand Up @@ -10211,6 +10211,16 @@ def test_partition_fp(N, dtype):
assert_arr_partitioned(np.sort(arr)[k], k,
arr[np.argpartition(arr, k, kind='introselect')])

# Check that `np.inf < np.nan`
# This follows np.sort
arr[0] = np.nan
arr[1] = np.inf
o1 = np.partition(arr, -2, kind='introselect')
o2 = arr[np.argpartition(arr, -2, kind='introselect')]
for out in [o1,o2]:
assert_(np.isnan(out[-1]))
assert_equal(out[-2], np.inf)

def test_cannot_assign_data():
a = np.arange(10)
b = np.linspace(0, 1, 10)
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