8000 BUG operations involving MaskedArray with output given do not return output by mhvk · Pull Request #8416 · numpy/numpy · GitHub
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BUG operations involving MaskedArray with output given do not return output #8416

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ahaldane merged 1 commit into from
Feb 1, 2017
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BUG operations involving MaskedArray with output given do not return output #8416

ahaldane merged 1 commit into from
Feb 1, 2017

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@mhvk mhvk commented Jan 22, 2017 •
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EDIT -- turned into a PR.

Fixes an inconsistency found in #8414:

import numpy as np
a = np.ma.MaskedArray([1., 2.])
b = np.ma.MaskedArray(1.)
c = a.sum(out=b)
c is b
# True
d = np.true_divide(c, 2., out=b)
d is b
# False

Here, d is b should be True. That it is Falses suggested __array_wrap__ is not implemented quite correctly, probably missing a special path for if self is obj -- this PR fixes that.

@mhvk mhvk mentioned this pull request Dec 24, 2016
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@mhvk mhvk mentioned this pull request Jan 21, 2017
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mhvk commented Jan 22, 2017

I turned this into a PR to fix the issue that ufunc(ma, out=ma) would not return ma. cc @juliantaylor and @charris who noticed this in #8414.

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mhvk commented Jan 22, 2017
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Note: probably this is better done in __array_prepare__, but given that we hopefully soon have __array_func__ to work with, I felt it not quite worth it to try to define that...

ahaldane
ahaldane reviewed Feb 1, 2017
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I just spent a little bit of effort trying to figure out if this copy had any purpose, but I can't see any. It's not related to the copying of masks discussed in #5580, for example.

Want to just remove it?

@mhvk
BUG Ensure that operations on MaskedArray return any output given.
7927b3c 
Without this commit, after an operation like
```
a = np.ma.MaskedArray([1., 2., 3.])
b = np.add(a, 1., out=a)
```
one would have `b is not a`.  With this PR, it is guaranteed that
`b is a`.
@mhvk mhvk force-pushed the ma/ensure-given-output-is-returned branch from 6640387 to 7927b3c Compare February 1, 2017 19:39
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mhvk commented Feb 1, 2017

@ahaldane - OK, I agree it made little sence so just removed the strange copy (and rebased). Hopefully, tests will still pass.

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ahaldane commented Feb 1, 2017

Looks good to me otherwise, merging. Thanks @mhvk

@ahaldane ahaldane merged commit a12a171 into numpy:master Feb 1, 2017
@mhvk mhvk deleted the ma/ensure-given-output-is-returned branch February 1, 2017 21:36
juliantaylor added a commit to juliantaylor/numpy that referenced this pull request Feb 6, 2017
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MAINT: remove ma out= workaround
6bb3fc4 
unnecessary since numpygh-8416
@juliantaylor juliantaylor mentioned this pull request Feb 6, 2017
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