I am currently running numpy rc2 (I haven't tried your
reimplementation yet as I am still using python 2.3). I am wondering
whether the new maskedarray is able to handle construction of arrays
from masked scalar values (not sure if this is the correct term). I
ran across a situation recently when I was picking individual values
from a masked array, collecting them in a list and then subsequently
constructing an array with these values. This does not work if any of
the values choosen are masked. See example below
On a more general note I am interested to find out whether there are
any other languages that handle masked/missing data well and if so how
this is done. My only experience is with R, which I have found to be
quite good (there is a special value NA this signifies a masked value
- this can be mixed in with non-masked values when defining an array).
from numpy import *
a = ma.array([1,2,3], mask=[True, False, False])
print a[0], type(a[0])
print a[1], type(a[1])
print list(a)
a = ma.array(list(a))
-- output --
--
Folks, I just posted on the scipy/developers zone wiki (http://projects.scipy.org/scipy/numpy/wiki/MaskedArray) a reimplementation of the masked_array mopdule, motivated by some problems I ran into while subclassing MaskedArray.
The main differences with the initial numpy.core.ma package are that MaskedArray is now a subclass of ndarray and that the _data section can now be any subclass of ndarray (well, it should work in most cases, some tweaking might required here and there). Apart from a couple of issues listed below, the behavior of the new MaskedArray class reproduces the old one. It is quite likely to be significantly slower, though: I was more interested in a clear organization than in performance, so I tended to use wrappers liberally. I'm sure we can improve that rather easily.
The new module, along with a test suite and some utilities, are available here: http://projects.scipy.org/scipy/numpy/attachment/wiki/MaskedArray/maskedarra... http://projects.scipy.org/scipy/numpy/attachment/wiki/MaskedArray/masked_tes... http://projects.scipy.org/scipy/numpy/attachment/wiki/MaskedArray/test_maske...
Please note that it's still a work in progress (even if it seems to work quite OK when I use it). Suggestions, comments, improvements and general feedback are more than welcome !
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