[Numpy-discussion] Re: empty_like for masked arrays

Pierre GM pgmdevlist at gmail.com
Tue Jun 11 04:21:59 EDT 2013

On June 11, 2013 at 00:40:31, Pierre GM (pgmdevlist at gmail.com) wrote:
On June 10, 2013 at 23:07:24 , Eric Firing (efiring at hawaii.edu) wrote:  
On 2013/06/10 10:17 AM, Aldcroft, Thomas wrote:  
> I use np.ma <http://np.ma>, and for me the most intuitive would be the  
> second option where the new array matches the original array in shape  
> and dtype, but always has an empty mask. I always think of the *_like()  
> functions as just copying shape and dtype, so it would be a bit  
> surprising to get part of the data (the mask) from the original. If you  
> do need the mask then on the next line you have an explicit statement to  
> copy the mask and the code and intent will be clear. Also, most of the  
> time the mask is set because that particular data value was bad or  
> missing, so it seems like it would be a less-common use case to want a  
> new empty array with the same mask.  

I also use np.ma (and it is used internally in matplotlib). I agree  
with Tom. I think all of the *_like() functions should start with  
mask=False, meaning nothing is masked by default. I don't see what the  
reasonable use cases would be for any alternative.  

Thinking about it, a replacement to `_convert2ma` should work something like

The `input.view(np.ndarray)` will get the `.data` part of a MaskedArray and work seamlessly with a regular ndarray, the `.view(MaskedArray)` will attach a `np.ma.nomask` to the result of the previous view (therefore making the output a MaskedArray). Depending on your decision, we could add a flag to copy the initial mask (if any)
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