[Numpy-discussion] np.diff on boolean arrays now raises

Charles R Harris charlesr.harris at gmail.com
Thu Jun 15 08:16:16 EDT 2017

On Thu, Jun 15, 2017 at 4:35 AM, Ralf Gommers <ralf.gommers at gmail.com>

> On Thu, Jun 15, 2017 at 7:08 PM, Jaime Fernández del Río <
> jaime.frio at gmail.com> wrote:
>> There is an ongoing discussion on github:
>> https://github.com/numpy/numpy/issues/9251
>> In 1.13 np.diff has started raising on boolean arrays, since subtraction
>> of  boolean arrays is now deprecated.
>> A decision has to be made whether:
>>    - raising an error is the correct thing to do, and only the docstring
>>    needs updating, or
>>    - backwards compatibility is more important and diff should still
>>    work on boolean arrays.
> The issue is bigger than np.diff. For example, there's a problem with the
> scipy.ndimage morphology functions (https://github.com/scipy/
> scipy/issues/7493) that looks pretty serious. All ndimage.binary_*
> functions (7 of them) for example return boolean arrays, and chaining those
> is now broken. Unfortunately it seems that that wasn't covered by the
> ndimage test suite.
> Possibly reverting the breaking change in 1.13.1 is the best way to fix
> this.

There were two related deprecations of boolean operators: subtraction and
negative. I haven't heard any complaints about the second, which I think is
less controversial, but I think reversion is the way to go for subtraction,
at least for 1.13.1. The main virtue of the deprecations is clarity, xor is
more informative when applied to boolean values than `-`, although the
latter is certainly correct in F_2.

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