[Numpy-discussion] missing data discussion round 2

Eric Firing efiring@hawaii....
Wed Jun 29 16:21:07 CDT 2011

On 06/29/2011 09:32 AM, Matthew Brett wrote:
> Hi,
> Clearly there are some overlaps between what masked arrays are trying
> to achieve and what Rs NA mechanisms are trying to achieve.  Are they
> really similar enough that they should function using the same API?
> And if so, won't that be confusing?  I think that's the question
> that's being asked.

And I think the answer is "no".  No more confusing to people coming from 
R to numpy than views already are--with or without the NEP--and not 
*requiring* people to use any NA-related functionality beyond what they 
are used to from R.

My understanding of the NEP is that it directly yields an API closely 
matching that of R, but with the opportunity, via views, to do more with 
less work, if one so desires.  The present masked array module could be 
made more efficient if the NEP is implemented; regardless of whether 
this is done, the masked array module is not about to vanish, so anyone 
wanting precisely the masked array API will have it; and others remain 
free to ignore it (except for those of us involved in developing 
libraries such as matplotlib, which will have to support all variations 
of the new API along with the already-supported masked arrays).

In addition, for new code, the full-blown masked array module may not be 
needed.  A convenience it adds, however, is the automatic masking of 
invalid values:

In [1]: np.ma.log(-1)
Out[1]: masked

I'm sure this horrifies some, but there are times and places where it is 
a genuine convenience, and preferable to having to use a separate 
operation to replace nan or inf with NA or whatever it ends up being.

If np.seterr were extended to allow such automatic masking as an option, 
then the need for a separate masked array module would shrink further. 
I wouldn't mind having to use an explicit kwarg for ignoring NA in 
reduction methods.


> See you,
> Matthew
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