[Numpy-discussion] numpy masked array oddity

Pierre GM pgmdevlist@gmail....
Mon May 5 14:23:03 CDT 2008


On Monday 05 May 2008 15:10:56 Eric Firing wrote:
> Pierre GM wrote:
> > * An alternative would be to force the output of MaskedArray.compressed()
> > to type(MaskedArray._baseclass), where the _baseclass attribute is the
> > class of the underlying array: usually it's only ndarray, but it can be
> > any subclass. Changing this behavior would not break anything in
> > TimeSeries.
>
> This alternative makes sense to me--I expect most use cases would be
> most efficient with compressed yielding a plain ndarray.  I don't see
> any gain in keeping it as a masked array, and having to manually convert
> it.  (I don't see how the _baseclass conversion would work with the
> baseclass as a matrix, though.)

In fact, it's straightforward:
- ravel the _data part to get a type(_baseclass) object
- use .compress on the _data part, using logical_not(mask) as the condition.
When you have a matrix as _baseclass, the result will be a ravelled version of 
the initial matrix.

But yes, it makes indeed more sense not to have a MaskedArray in output. 
SVN5126 should now work as discussed.



> Eric
>
> > * I need to fix a bug in compressed when the underlying array is a
> > matrix: I can take care of the alternative at the same time. What are the
> > opinions on that matter ?
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