[Numpy-discussion] Make np.bincount output same dtype as weights

[Jaime Fernández del Río]

Have modified the PR to do the "promote integers to at least long" we do in
np.sum.

Jaime

On Mon, Mar 28, 2016 at 9:55 PM, CJ Carey <perimosocordiae at gmail.com> wrote:

> Another +1 for Josef's interpretation from me. Consistency with np.sum
> seems like the best option.
>
> On Sat, Mar 26, 2016 at 11:12 PM, Juan Nunez-Iglesias <jni.soma at gmail.com>
> wrote:
>
>> Thanks for clarifying, Jaime, and fwiw I agree with Josef: I would expect
>> np.bincount to behave like np.sum with regards to promoting weights dtypes.
>> Including bool.
>>
>> On Sun, Mar 27, 2016 at 1:58 PM, <josef.pktd at gmail.com> wrote:
>>
>>> On Sat, Mar 26, 2016 at 9:54 PM, Joseph Fox-Rabinovitz
>>> <jfoxrabinovitz at gmail.com> wrote:
>>> > Would it make sense to just make the output type large enough to hold
>>> the
>>> > cumulative sum of the weights?
>>> >
>>> >
>>> > - Joseph Fox-Rabinovitz
>>> >
>>> > ------ Original message------
>>> >
>>> > From: Jaime Fernández del Río
>>> >
>>> > Date: Sat, Mar 26, 2016 16:16
>>> >
>>> > To: Discussion of Numerical Python;
>>> >
>>> > Subject:[Numpy-discussion] Make np.bincount output same dtype as
>>> weights
>>> >
>>> > Hi all,
>>> >
>>> > I have just submitted a PR (#7464) that fixes an enhancement request
>>> > (#6854), making np.bincount return an array of the same type as the
>>> weights
>>> > parameter.  This is an important deviation from current behavior, which
>>> > always casts weights to double, and always returns a double array, so I
>>> > would like to hear what others think about the worthiness of this.
>>> Main
>>> > discussion points:
>>> >
>>> > np.bincount now works with complex weights (yay!), I guess this should
>>> be a
>>> > pretty uncontroversial enhancement.
>>> > The return is of the same type as weights, which means that small
>>> integers
>>> > are very likely to overflow.  This is exactly what #6854 requested, but
>>> > perhaps we should promote the output for integers to a long, as we do
>>> in
>>> > np.sum?
>>>
>>> I always thought of bincount with weights just as a group-by sum. So
>>> it would be easier to remember and have fewer surprises if it matches
>>> the behavior of np.sum.
>>>
>>> > Boolean arrays stay boolean, and OR, rather than sum, the weights. Is
>>> this
>>> > what one would want? If we decide that integer promotion is the way to
>>> go,
>>> > perhaps booleans should go in the same pack?
>>>
>>> Isn't this calculating the sum, i.e. count of True by group, already?
>>> Based on a quick example with numpy 1.9.2, I don't think I ever used
>>> bool weights before.
>>>
>>>
>>> > This new implementation currently supports all of the reasonable native
>>> > types, but has no fallback for user defined types.  I guess we should
>>> > attempt to cast the array to double as before if no native loop can be
>>> > found? It would be good to have a way of testing this though, any
>>> thoughts
>>> > on how to go about this?
>>> > Does a behavior change like this require some deprecation period? What
>>> would
>>> > that look like?
>>> > I have also added broadcasting of weights to the full size of list, so
>>> that
>>> > one can do e.g. np.bincount([1, 2, 3], weights=2j) without having to
>>> tile
>>> > the single weight to the size of the bins list.
>>> >
>>> > Any other thoughts are very welcome as well!
>>>
>>> (2-D weights ?)
>>>
>>>
>>> Josef
>>>
>>>
>>> >
>>> > Jaime
>>> >
>>> > --
>>> > (__/)
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>>> > dominación mundial.
>>> >
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>>
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