On Mo, 2015-01-26 at 02:02 -0800, Jaime Fernández del Río wrote: > On Mon, Jan 26, 2015 at 1:41 AM, Sebastian Berg > <sebast...@sipsolutions.net> wrote: > On Mo, 2015-01-26 at 09:24 +0100, Jens Jørgen Mortensen wrote: > > Hi! > > > > I have a view of a 2-d complex array that I would like to > view as a 2-d > > float array. This works OK: > > > > >>> np.ones((2, 4), complex).view(float) > > array([[ 1., 0., 1., 0., 1., 0., 1., 0.], > > [ 1., 0., 1., 0., 1., 0., 1., 0.]]) > > > > but this doesn't: > > > > >>> np.ones((2, 4), complex)[:, :2].view(float) > > Traceback (most recent call last): > > File "<stdin>", line 1, in <module> > > ValueError: new type not compatible with array. > > >>> np.__version__ > > '1.9.0' > > > > and I don't understand why. When looking at the memory > layout, I think > > it should be possible. > > > > Yes, it should be possible, but it is not :). You could hack > it by using > `np.ndarray` (or stride tricks). Or maybe you are interested > making the > checks whether it makes sense or not less strict. > > > How would it be possible? He goes from an array with 16 byte strides > along the last axis: >
Oh, sorry, you are right of course. I thought it was going the other way around, from double -> complex. That way could work (in this case I think), but does not currently. > > r0i0, r1i1, r2i2, r3i3 > > > to one with 32 byte strides, which is OK > > > r0i0, xxxx, r2i2, xxxx > > > but everything breaks down when he wants to have alternating strides > of 8 and 24 bytes: > > > r0, i0, xxxx, r2, i2, xxxx > > > which cannot be hacked in any sensible way. > > > What I think could be made to work, but also fails, is this: > > > np.ones((2, 4), complex).reshape(2, 4, 1)[:, :2, :].view(float) > > > > Here the original strides are (64, 16, xx) and the resulting view > should have strides (64, 32, 8), not sure what trips this. > > > Jaime > > > > - Sebastian > > > Jens Jørgen > > > > _______________________________________________ > > NumPy-Discussion mailing list > > NumPy-Discussion@scipy.org > > http://mail.scipy.org/mailman/listinfo/numpy-discussion > > > > _______________________________________________ > NumPy-Discussion mailing list > NumPy-Discussion@scipy.org > http://mail.scipy.org/mailman/listinfo/numpy-discussion > > > > > > -- > (\__/) > ( O.o) > ( > <) Este es Conejo. Copia a Conejo en tu firma y ayúdale en sus > planes de dominación mundial. > _______________________________________________ > NumPy-Discussion mailing list > NumPy-Discussion@scipy.org > http://mail.scipy.org/mailman/listinfo/numpy-discussion
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