[Numpy-discussion] masked arrays of structured arrays

Ernest Adrogué eadrogue@gmx....
Sat Aug 22 06:58:44 CDT 2009

Hi there,

Here is a structured array with 3 fields each of which has 3 fields
in turn:

In [3]: desc = [('a',int), ('b',int), ('c',int)]

In [4]: desc = [('x',desc), ('y',desc), ('z',desc)]

With a regular ndarray it works just fine:

In [11]: x = np.zeros(2, dtype=desc)

In [12]: x['x']['b'] = 2

In [13]: x['x']['b']
Out[13]: array([2, 2])

However if try the same with a masked array, it fails:

In [14]: x = np.ma.masked_all(2, dtype=desc)

In [15]: x['x']['b'] = 2
ValueError                                Traceback (most recent call last)

/home/ernest/<ipython console> in <module>()

/usr/lib/python2.5/site-packages/numpy/ma/core.pyc in __setitem__(self, indx, value)
   1574             if self._mask is nomask:
   1575                 self._mask = make_mask_none(self.shape, self.dtype)
-> 1576             ndarray.__setitem__(self._mask, indx, getmask(value))
   1577             return
   1578         #........................................

ValueError: field named b not found.

Any idea of what the problem is?


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