[Numpy-discussion] consensus (was: NA masks in the next numpy release?)

Charles R Harris charlesr.harris@gmail....
Sat Oct 29 17:10:21 CDT 2011


On Sat, Oct 29, 2011 at 4:02 PM, Olivier Delalleau <shish@keba.be> wrote:

> 2011/10/29 Ralf Gommers <ralf.gommers@googlemail.com>
>
>>
>>
>> On Sat, Oct 29, 2011 at 11:36 PM, Matthew Brett <matthew.brett@gmail.com>wrote:
>>
>>> Hi,
>>>
>>> On Sat, Oct 29, 2011 at 1:48 PM, Matthew Brett <matthew.brett@gmail.com>
>>> wrote:
>>> > Hi,
>>> >
>>> > On Sat, Oct 29, 2011 at 1:44 PM, Ralf Gommers
>>> > <ralf.gommers@googlemail.com> wrote:
>>> >>
>>> >>
>>> >> On Sat, Oct 29, 2011 at 9:04 PM, Matthew Brett <
>>> matthew.brett@gmail.com>
>>> >> wrote:
>>> >>>
>>> >>> Hi,
>>> >>>
>>> >>> On Sat, Oct 29, 2011 at 3:26 AM, Ralf Gommers
>>> >>> <ralf.gommers@googlemail.com> wrote:
>>> >>> >
>>> >>> >
>>> >>> > On Sat, Oct 29, 2011 at 1:37 AM, Matthew Brett <
>>> matthew.brett@gmail.com>
>>> >>> > wrote:
>>> >>> >>
>>> >>> >> Hi,
>>> >>> >>
>>> >>> >> On Fri, Oct 28, 2011 at 4:21 PM, Ralf Gommers
>>> >>> >> <ralf.gommers@googlemail.com> wrote:
>>> >>> >> >
>>> >>> >> >
>>> >>> >> > On Sat, Oct 29, 2011 at 12:37 AM, Matthew Brett
>>> >>> >> > <matthew.brett@gmail.com>
>>> >>> >> > wrote:
>>> >>> >> >>
>>> >>> >> >> Hi,
>>> >>> >> >>
>>> >>> >> >> On Fri, Oct 28, 2011 at 3:14 PM, Charles R Harris
>>> >>> >> >> <charlesr.harris@gmail.com> wrote:
>>> >>> >> >> >>
>>> >>> >> >>
>>> >>> >> >> No, that's not what Nathaniel and I are saying at all.
>>> Nathaniel was
>>> >>> >> >> pointing to links for projects that care that everyone agrees
>>> before
>>> >>> >> >> they go ahead.
>>> >>> >> >
>>> >>> >> > It looked to me like there was a serious intent to come to an
>>> >>> >> > agreement,
>>> >>> >> > or
>>> >>> >> > at least closer together. The discussion in the summer was going
>>> >>> >> > around
>>> >>> >> > in
>>> >>> >> > circles though, and was too abstract and complex to follow.
>>> Therefore
>>> >>> >> > Mark's
>>> >>> >> > choice of implementing something and then asking for feedback
>>> made
>>> >>> >> > sense
>>> >>> >> > to
>>> >>> >> > me.
>>> >>> >>
>>> >>> >> I should point out that the implementation hasn't - as far as I
>>> can
>>> >>> >> see - changed the discussion.  The discussion was about the API.
>>> >>> >>
>>> >>> >> Implementations are useful for agreed APIs because they can point
>>> out
>>> >>> >> where the API does not make sense or cannot be implemented.  In
>>> this
>>> >>> >> case, the API Mark said he was going to implement - he did
>>> implement -
>>> >>> >> at least as far as I can see.  Again, I'm happy to be corrected.
>>> >>> >
>>> >>> > Implementations can also help the discussion along, by allowing
>>> people
>>> >>> > to
>>> >>> > try out some of the proposed changes. It also allows to construct
>>> >>> > examples
>>> >>> > that show weaknesses, possibly to be solved by an alternative API.
>>> Maybe
>>> >>> > you
>>> >>> > can hold the complete history of this topic in your head and
>>> comprehend
>>> >>> > it,
>>> >>> > but for me it would be very helpful if someone said:
>>> >>> > - here's my dataset
>>> >>> > - this is what I want to do with it
>>> >>> > - this is the best I can do with the current implementation
>>> >>> > - here's how API X would allow me to solve this better or simpler
>>> >>> > This can be done much better with actual data and an actual
>>> >>> > implementation
>>> >>> > than with a design proposal. You seem to disagree with this
>>> statement.
>>> >>> > That's fine. I would hope though that you recognize that concrete
>>> >>> > examples
>>> >>> > help people like me, and construct one or two to help us out.
>>> >>> That's what use-cases are for in designing APIs.  There are examples
>>> >>> of use in the NEP:
>>> >>>
>>> >>> https://github.com/numpy/numpy/blob/master/doc/neps/missing-data.rst
>>> >>>
>>> >>> the alterNEP:
>>> >>>
>>> >>> https://gist.github.com/1056379
>>> >>>
>>> >>> and my longer email to Travis:
>>> >>>
>>> >>>
>>> >>>
>>> http://article.gmane.org/gmane.comp.python.numeric.general/46544/match=ignored
>>> >>>
>>> >>> Mark has done a nice job of documentation:
>>> >>>
>>> >>> http://docs.scipy.org/doc/numpy/reference/arrays.maskna.html
>>> >>>
>>> >>> If you want to understand what the alterNEP case is, I'd suggest the
>>> >>> email, just because it's the most recent and I think the terminology
>>> >>> is slightly clearer.
>>> >>>
>>> >>> Doing the same examples on a larger array won't make the point easier
>>> >>> to understand.  The discussion is about what the right concepts are,
>>> >>> and you can help by looking at the snippets of code in those
>>> >>> documents, and deciding for yourself whether you think the current
>>> >>> masking / NA implementation seems natural and easy to explain, or
>>> >>> rather forced and difficult to explain, and then email back trying to
>>> >>> explain your impression (which is not always easy).
>>> >>
>>> >> If you seriously believe that looking at a few snippets is as helpful
>>> and
>>> >> instructive as being able to play around with them in IPython and
>>> modify
>>> >> them, then I guess we won't make progress in this part of the
>>> discussion.
>>> >> You're just telling me to go back and re-read things I'd already read.
>>> >
>>> > The snippets are in ipython or doctest format - aren't they?
>>>
>>> Oops - 10 minute rule.  Now I see that you mean that you can't
>>> experiment with the alternative implementation without working code.
>>>
>>
>> Indeed.
>>
>>
>>> That's true, but I am hoping that the difference between - say:
>>>
>>> a[0:2] = np.NA
>>>
>>> and
>>>
>>> a.mask[0:2] = False
>>>
>>> would be easy enough to imagine.
>>
>>
>> It is in this case. I agree the explicit ``a.mask`` is clearer. This is a
>> quite specific point that could be improved in the current implementation.
>> It doesn't require ripping everything out.
>>
>> Ralf
>>
>
> I haven't been following the discussion closely, but wouldn't it be
> instead:
> a.mask[0:2] = True?
>
> It's something that I actually find a bit difficult to get right in the
> current numpy.ma implementation: I would find more intuitive to have True
> for "valid" data, and False for invalid / missing / ... I realize how the
> implementation makes sense (and is appropriate given that the name is
> "mask"), but I just thought I'd point this out... even if it's just me ;)
>
>
Well, there is the problem of replacing an unknown value by a known value,
and then you would have to clear the mask also. However, I do appreciate
this sort of feedback from actual use. We need more in order to see what are
real sticking points and to separate the usual frustrations of learning new
stuff from the more serious problem of inadequate API. If enough people
start giving feedback we might want to set up some way to track it.

Chuck
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