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take slower when out is provided #28636
Description
Describe the issue:
I've noticed this when trying to use the C-API PyArray_TakeFrom but it can be shown using python as well:
import numpy as np
print(np.__version__)
# 2.2.4
x = np.arange(85, dtype=float)
idxs = np.repeat(np.arange(85), 110)
out = np.empty_like(np.take(x, idxs, out=None))
%timeit np.take(x, idxs, out=None)
%timeit np.take(x, idxs, out=out)
# 6.76 μs ± 106 ns per loop (mean ± std. dev. of 7 runs, 100,000 loops each)
# 8.99 μs ± 30.8 ns per loop (mean ± std. dev. of 7 runs, 100,000 loops each)With those sizes, I would expect the overhead to be mostly from copying the values, not checking whether the provided output is valid.
Python and NumPy Versions:
numpy 2.2.4, python 3.12.8
Runtime Environment:
No response
Context for the issue:
No response
Activity
[-]`numpy_take` slower when `out` is provided[/-][+]`take` slower when `out` is provided[/+]ngoldbaum commentedon Apr 3, 2025
I see the same thing on my Mac:
Let me see if I can get samply to give me a useful profile so we can understand where the difference is.
ngoldbaum commentedon Apr 3, 2025
The difference is that using
outleads to a code path that does a copy. I'm not sure offhand why a copy is necessary here.with
out:without:
EDIT: (also pretty neat that you can get Python frames in samply profiles!)
seberg commentedon Apr 3, 2025
The reason is that
takeensures that the output is unchanged when an out-of-bounds access happens.That is how it has always been, I don't disagree that this is likely not needed. Not sure about changing it, but I would be OK if a few people are in favor (with a release note).
EDIT: I.e.
mode="wrap"makes this go away.ricardoV94 commentedon Apr 3, 2025
I would like to have it raise still. If anybody objects to changing the behavior could we instead have an additional raise+mutate mode instead?
seberg commentedon Apr 4, 2025
Let's bring it up at the triage meeting. I am carefully in favor of just changing it with a release note. It just feels like
out=is usually for speed, and you can useout[...] = take(arr, idx).So, if you are interested in this, I think this is likely enough to happen that opening a PR for it is useful.
(Adding a
modeseems a lot of addition for nothing to me.)ricardoV94 commentedon Apr 4, 2025
Totally agree
mattip commentedon Aug 20, 2025
We discussed this at a triage meeting and would like to see a PR to implement the idea of avoiding a copy.
Ijtihed commentedon Jul 8, 2026
I can take a look at and implement this. gut feeling says it'll be easy and quite a performance boost. let's see!