[Numpy-discussion] Is this an indexing bug?
Sturla Molden
sturla@molden...
Tue Jun 19 05:35:05 CDT 2007
On 6/19/2007 12:14 PM, Sturla Molden wrote:
> h[0,:,numpy.arange(14)] is a case of "sdvanced indexing". You can also
> see that
>
> >>> h[0,:,[0,1,2,3,4,5,6,7,8,9,10,11,12,13]].shape
> (14, 4)
Another way to explain this is that numpy.arange(14) and
[0,1,2,3,4,5,6,7,8,9,10,11,12,13] is a sequence (i.e. iterator). So
when NumPy iterates the sequence, the iterator yields a single integer,
lets call it I. Using this integer as an index to h, gives a = h[0,:,I]
which has shape=(4,). This gives us a sequence of arrays of length 4. In
other words,
>>> a = numpy.zeros(4)
>>> numpy.array([a,a,a,a,a,a,a,a,a,a,a,a,a,a]).shape
(14, 4)
That is analogous to
array([(0,0,0,0), (0,0,0,0), ...., (0,0,0,0)])
Sturla Molden
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