[Numpy-discussion] indexing bug in numpy r2694

Pau Gargallo pau.gargallo at gmail.com
Wed Jun 28 12:40:35 CDT 2006


i don't know why 'where' is returning matrices.
if you use:

>>> idx = where(y.A > 0.5)[0]

everything will work fine (I guess)

pau


On 6/28/06, Keith Goodman <kwgoodman at gmail.com> wrote:
> >> x = asmatrix(rand(3,2))
>
> >> y = asmatrix(rand(3,1))
>
> >> y
>
> matrix([[ 0.77952062],
>        [ 0.97110465],
>        [ 0.77450218]])
>
> >> idx = where(y > 0.5)[0]
>
> >> idx
> matrix([[0, 1, 2]])
>
> >> x[idx,:]
>
> matrix([[ 0.24837887,  0.52988253],
>        [ 0.28661085,  0.43053076],
>        [ 0.05360893,  0.22668509]])
>
> So far everything works as it should. Now the problem:
>
> >> y[idx,:]
> ---------------------------------------------------------------------------
> exceptions.ValueError                                Traceback (most
> recent call last)
>
> /usr/local/lib/python2.4/site-packages/numpy/core/defmatrix.py in
> __getitem__(self, index)
>     120
>     121     def __getitem__(self, index):
> --> 122         out = N.ndarray.__getitem__(self, index)
>     123         # Need to swap if slice is on first index
>     124         retscal = False
>
> /usr/local/lib/python2.4/site-packages/numpy/core/defmatrix.py in
> __array_finalize__(self, obj)
>     116             self.shape = (1,1)
>     117         elif ndim == 1:
> --> 118             self.shape = (1,self.shape[0])
>     119         return
>     120
>
> ValueError: total size of new array must be unchanged
>
>
> And, on a related note, shouldn't this be a column vector?
>
> >> x[idx,0]
> matrix([[ 0.24837887,  0.28661085,  0.05360893]])
>
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