[Numpy-discussion] MA and iterators

[Andrew McNamara]

I did some benchmarking today and discovered that iterating over MA
arrays is 14 times slower than iterating over a Numeric array (or a
python list). One simple solution to this is to add iterator support to
the MaskedArray class. To prove the principle, I patched MaskedArray on
the fly:

    import MA

    def ma__iter__(self):
        "Get an MA iterator."
        def scaler_iter(d, m):
            for i, v in enumerate(d):
                if m[i]:
                    v = masked
                yield v
        def array_iter(d, m, fill_value):
            ss = d.spacesaver()
            tc = d.typecode()
            for i, v in enumerate(d):
                yield MA.array(v, typecode=tc, copy=1, savespace=ss, 
                               mask=m[i], fill_value=fill_value)
        if self._mask is None:
            return iter(self._data)
        if len(self.shape) > 1:
            return array_iter(self._data, self._mask)
        else:
            return scalar_iter(self._data, self._mask, self.fill_value())

    MA.MaskedArray.__iter__ = ma__iter__

Note that this implementation requires generator support.

-- 
Andrew McNamara, Senior Developer, Object Craft
http://www.object-craft.com.au/