[Numpy-discussion] feedback request: proposal to add masks to the core ndarray
Thu Jun 23 16:55:00 CDT 2011
On Thu, Jun 23, 2011 at 4:46 PM, Charles R Harris <firstname.lastname@example.org
> On Thu, Jun 23, 2011 at 2:53 PM, Mark Wiebe <email@example.com> wrote:
>> Enthought has asked me to look into the "missing data" problem and how
>> NumPy could treat it better. I've considered the different ideas of adding
>> dtype variants with a special signal value and masked arrays, and concluded
>> that adding masks to the core ndarray appears is the best way to deal with
>> the problem in general.
>> I've written a NEP that proposes a particular design, viewable here:
>> There are some questions at the bottom of the NEP which definitely need
>> discussion to find the best design choices. Please read, and let me know of
>> all the errors and gaps you find in the document.
> I agree that low level support for masks is the way to go.
> > If all the input values are masked, 'sum' and 'prod' will produce the
> additive and multiplicative identities respectively
> A masked zero dimensional array might be another option, depending on how
> you handle scalars. This would also work when arrays were summed down an
> axis if a masked array was returned.
I think there has to be a difference like with "sum" and "nansum". Maybe
control over this would be a parameter to the sum function, indicating how
to interpret masked values.
> I suppose the problem with using the word 'mask' is the implication that it
> hides something. Maybe 'window' would be an alternate choice, although in
> this context I tend to think of 'mask' as having the meaning you assign to
Some copy/paste from the NEP:
There is some consternation about the conventional True/False
interpretation of the mask, centered around the name "mask". One
possibility to deal with this is to call it a "validity mask" in
all documentation, which more clearly indicates that True means
valid data. If this isn't sufficient, an alternate name for the
attribute could be found, like "a.validitymask", "a.validmask",
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