[Numpy-discussion] MaskedArray compatibility decorators

18 May 2015

      Hello,

I created 2 decorators for improve compatibility of "numpy.ma.MaskedArray"
with functions that don't support them.

This simply convert MaskedArray to classical ndarray with masked value
converted to NaN, use the function, and reconvert to MaskedArray.

@MaArrayToNaNKeepMask : Re-use the source mask on the output.
@MaArrayToNaNFixInvalid : Replace invalid values by mask on the output.

Source: 

    import numpy as np

    def MaArrayToNaNKeepMask(func):
        """
        MaArray to ndArray with nan decorator.

        Keep mask from originale ndArray.
        """
        def wrapper(MaArray, *args, **kwargs):
            try:
                Mask = MaArray.mask
                fill = MaArray.fill_value
                return np.ma.masked_array(func(MaArray.filled(np.NaN),*args,
**kwargs), mask=Mask, fill_value=fill)
            except:
                return func(MaArray, *args, **kwargs)
        return wrapper

def MaArrayToNaNFixInvalid(func):
    """
    MaArray to ndArray with nan decorator.

    Recreate mask from invalid points.
    """
    def wrapper(MaArray, *args, **kwargs):
        try:
            fill = MaArray.fill_value
            return np.ma.fix_invalid(func(MaArray.filled(np.NaN), *args,
**kwargs), fill_value=fill)
        except:
            return func(MaArray, *args, **kwargs)
    return wrapper

Exemple: 

import skimage.transform

@MaArrayToNaNFixInvalid
def maresize(image, output_shape, order=1, mode='constant', cval=0,
clip=True, preserve_range=True):
    return skimage.transform.resize(image, output_shape, order, mode, cval,
clip, preserve_range)

I think it may be usefull to include this directly on numpy. There is a lot
of functions that don't work directly with MaskedArray.

[Numpy-discussion] MaskedArray compatibility decorators

J.Goutin