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astype converts numpy array values to 0.0 for structured dtype #7058

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mpconte opened this issue Jan 18, 2016 · 5 comments
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astype converts numpy array values to 0.0 for structured dtype #7058

mpconte opened this issue Jan 18, 2016 · 5 comments
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54 - Needs decision component: numpy._core

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@mpconte
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mpconte commented Jan 18, 2016

import numpy as np

dtype = np.dtype([('Point', 'f', (3,))])
ones = np.ones(1, dtype=dtype) --> array([([1.0, 1.0, 1.0],)], dtype=[('Point', '<f4', (3,))])
flattened_dtype = np.dtype([('x', 'f'), ('y', 'f'), ('z', 'f')])
flat_ones = ones.astype(flattened_dtype) --> array([(0.0, 0.0, 0.0)], dtype=[('x', '<f4'), ('y', '<f4'), ('z', '<f4')])

numpy version 1.9.2
@charris
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charris commented Jan 18, 2016

Also in 1.11.

@ahaldane
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I will check when I get home, but I suspect this is another version of the long-standing bug which could be fixed by #6053. Specifically, I think this is example 'v3' in the example there: When numpy does not find a matching field-name on the lhs, it simply assigns 0 to the rhs field.

@ahaldane
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I'd also add, @mpconte's example is in some sense the current desired behavior: Assignment between two structures arrays currently works by matching up field names between the lhs and rhs. If a field name on the rhs is not present in the lhs, that field gets assigned 0. This is not documented anywhere, but there are comments in the code suggesting it is intentional.

If you want a real mind-bender, replaced flattened_dtype in your example by

flattened_dtype = np.dtype([('x', 'f'), ('Point', 'f'), ('z', 'f')])

@charris
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charris commented Jan 18, 2016

That makes sense.

@mpconte
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mpconte commented Jan 19, 2016

Thanks for the insight.
I also just discovered that using view instead of astype acutally gives me the result I'd expect, regardless of field names, thanks.

@ahaldane ahaldane mentioned this issue May 22, 2016
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ahaldane added a commit to ahaldane/numpy that referenced this issue Jun 17, 2016
@ahaldane
MAINT: improve struct assignment, allow multi fields views
2ef0103 
This commit attempts to make structure assignment more consistent, and
then changes multi-field indices to return a view instead of a copy.

Assignment between structures now works "by field position" rather than
"by field name".

Fixes numpy#2353, fixes numpy#6085, fixes numpy#3351, fixes numpy#6085, fixes numpy#6314,
fixes numpy#2346, fixes numpy#7058, fixes numpy#3641, fixes numpy#5994, fixes numpy#7262,
fixes numpy#7493
@charris charris closed this as completed in 7412b85 Sep 9, 2017
theodoregoetz pushed a commit to theodoregoetz/numpy that referenced this issue Oct 23, 2017
@ahaldane @theodoregoetz
MAINT: improve struct assignment, allow multi fields views
ae582a8 
This commit attempts to make structure assignment more consistent, and
then changes multi-field indices to return a view instead of a copy.

Assignment between structures now works "by field position" rather than
"by field name".

Fixes numpy#2353, fixes numpy#6085, fixes numpy#3351, fixes numpy#6085, fixes numpy#6314,
fixes numpy#2346, fixes numpy#7058, fixes numpy#3641, fixes numpy#5994, fixes numpy#7262,
fixes numpy#7493
@ahaldane ahaldane mentioned this issue Nov 16, 2017
Closed
@ahaldane ahaldane mentioned this issue Mar 15, 2018
Closed
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