[Numpy-discussion] in the NA discussion, what can we agree on?
Benjamin Root
ben.root@ou....
Fri Nov 4 22:45:00 CDT 2011
On Fri, Nov 4, 2011 at 10:33 PM, T J <tjhnson@gmail.com> wrote:
> On Fri, Nov 4, 2011 at 8:03 PM, Nathaniel Smith <njs@pobox.com> wrote:
>
>> On Fri, Nov 4, 2011 at 7:43 PM, T J <tjhnson@gmail.com> wrote:
>> > On Fri, Nov 4, 2011 at 6:31 PM, Pauli Virtanen <pav@iki.fi> wrote:
>> >> An acid test for proposed rules: given two arrays `a` and `b`,
>> >>
>> >> a = [1, 2, IGNORED(3), IGNORED(4)]
>> >> b = [10, IGNORED(20), 30, IGNORED(40)]
>> [...]
>> > (A1) Does unmask(a+b) == unmask(b + a) ?
>> >
>> > Yes. They both equal:
>> >
>> > unmask([11, IGNORED(22), IGNORED(33), IGNORED(44)])
>> > =
>> > [11, 22, 33, 44]
>>
>> Again, I really don't think you're going to be able to sell an API where
>> [2] + [IGNORED(20)] == [IGNORED(22)]
>> I mean, it's not me you have to convince, it's Gary, Pierre, maybe
>> Benjamin, Lluís, etc. So I could be wrong. But you might want to
>> figure that out first before making plans based on this...
>>
>
> But this is how np.ma currently does it, except that it doesn't compute
> the payload---it just calls it IGNORED.
> And it seems that this generalizes the way people want it to:
>
> >>> z = [2, 4] + [IGNORED(20), 3]
> >>> z
> [IGNORED(24), 7]
> >>> z.sum(skip_ignored=True) # True could be the default
> 7
> >>> z.sum(skip_ignored=False)
> IGNORED(31)
>
> I guess I am confused because it seems that you implicitly used this same
> rule here:
>
> Say we have
> >>> a = np.array([1, IGNORED(2), 3])
>
> >>> b = np.array([10, 20, 30])
> (Here's I'm using IGNORED(2) to mean a value that is currently
> ignored, but if you unmasked it it would have the value 2.)
>
> Then we have:
>
> # non-propagating **or** propagating, doesn't matter:
>
> >>> a + 2
>
> [3, IGNORED(2), 5]
>
>
> That is, element-wise, you had to have done:
>
> IGNORED(2) + 2 --> IGNORED(2).
>
> I said it should be equal to IGNORED(4), but the result is still some form
> of ignore. Sorry if I am missing the bigger picture at this point....its
> late and a Fri.
>
>
>
This scheme is actually somewhat intriguing. Not totally convinced, by
intrigued. Unfortunately, I fell behind in the postings by having
dinner... We probably should start a new thread soon with a bunch of this
stuff solidified and stated to give others a chance to hop back into the
game. Maybe a table of some sort with pros/cons (mathematically speaking,
deferring implementation details for later).
I swear, if we can get this to make sense... we should have a Nobel prize
or something.
Ben Root
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