[Numpy-discussion] Re: Using Reduce with Multi-dimensional Masked array

[Reggie Dugard]

> That raises the question of how to determine a count of valid values
> in a masked array.  Can I assume that I can do 'math' on the mask
> array itself, for example to sum along a given axis and have the
> masked cells add up?
>
> In my original example, I would expect a sum along the second axis
> to return [0,0,0,2,0].  Can I rely on this?  I would suggest that a
> .count operator would be very useful in working with masked arrays
> (count valid and count masked).

Actually masked arrays already have a count method that does what you
want:

Python 2.2b2 (#26, Nov 16 2001, 11:44:11) [MSC 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> from pydoc import help
>>> import MA
>>> x = MA.arange(10)
>>> help(x.count)
Help on method count in module MA.MA:

count(self, axis=None) method of MA.MA.MaskedArray instance
    Count of the non-masked elements in a, or along a certain axis.

>>> x.count()
10
>>>