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numpy.void and numpy.ma.mvoid with structured dtypes should support indexing with multiple fields #7262

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gerritholl opened this issue Feb 16, 2016 · 1 comment
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numpy.void and numpy.ma.mvoid with structured dtypes should support indexing with multiple fields #7262

gerritholl opened this issue Feb 16, 2016 · 1 comment

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@gerritholl
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A structured ndarray can be indexed with multiple fields:

In [14]: X = numpy.empty(shape=1, dtype="(2)3S,(2)3U")

In [15]: X[["f0","f1"]]
Out[15]: 
array([([b'', b''], ['', ''])], 
      dtype=[('f0', 'S3', (2,)), ('f1', '<U3', (2,))])

However, the corresponding numpy.void type cannot:

In [16]: X[0][["f0","f1"]]
---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
<ipython-input-16-4f230bb69b0d> in <module>()
----> 1 X[0][["f0","f1"]]

IndexError: invalid index

The same is true for masked arrays.

For consistently, numpy.void with a structured dtype should support indexing with multiple fields exactly like numpy.ndarray does.
@ahaldane
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I actually had fixed this in #6208, but I backpedaled because mutli-field subscripts work strangely (see #6053). My plan was to get #6053 in first, and then go back and enable this.

#6208 has already partially set up the fix: All that's left is to change the if(Py_Ustring_Check(ind) in voidtype_subscript to test for an array of strings too.

@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
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@gerritholl @ahaldane