numpy-discussion

[Numpy-discussion] indexing bug in numpy r2694

[Keith G. <kwg...@gm...>]

>> 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]])

Re: [Numpy-discussion] indexing bug in numpy r2694

[Pau G. <pau...@gm...>]

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 <kwg...@gm...> 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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Re: [Numpy-discussion] indexing bug in numpy r2694

[Keith G. <kwg...@gm...>]

On 6/28/06, Pau Gargallo <pau...@gm...> wrote:
> 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)

What about the second issue? Is this expected behavior?

>> idx
array([0, 1, 2])

>> y

matrix([[ 0.63731308],
       [ 0.34282663],
       [ 0.53366791]])

>> y[idx]

matrix([[ 0.63731308],
       [ 0.34282663],
       [ 0.53366791]])

>> y[idx,0]
matrix([[ 0.63731308,  0.34282663,  0.53366791]])

I was expecting a column vector.

Re: [Numpy-discussion] indexing bug in numpy r2694

[Pau G. <pau...@gm...>]

On 6/28/06, Keith Goodman <kwg...@gm...> wrote:
> On 6/28/06, Pau Gargallo <pau...@gm...> wrote:
> > 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)
>
> What about the second issue? Is this expected behavior?
>
> >> idx
> array([0, 1, 2])
>
> >> y
>
> matrix([[ 0.63731308],
>        [ 0.34282663],
>        [ 0.53366791]])
>
> >> y[idx]
>
> matrix([[ 0.63731308],
>        [ 0.34282663],
>        [ 0.53366791]])
>
> >> y[idx,0]
> matrix([[ 0.63731308,  0.34282663,  0.53366791]])
>
> I was expecting a column vector.
>
I have never played with matrices, but if y was an array, y[idx,0]
will be an array of the same shape of idx. That is a 1d array.
I guess that when y is a matrix, this 1d array is converted to a
matrix and become a row vector.

I don't know if this behaviour is wanted :-(

cheers,
pau

Re: [Numpy-discussion] indexing bug in numpy r2694

[Travis O. <oli...@ee...>]

Keith Goodman wrote:

>On 6/28/06, Pau Gargallo <pau...@gm...> wrote:
>  
>
>>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)
>>    
>>
>
>What about the second issue? Is this expected behavior?
>
>  
>
>>>idx
>>>      
>>>
>array([0, 1, 2])
>
>  
>
>>>y
>>>      
>>>
>
>matrix([[ 0.63731308],
>       [ 0.34282663],
>       [ 0.53366791]])
>
>  
>
>>>y[idx]
>>>      
>>>
>
>matrix([[ 0.63731308],
>       [ 0.34282663],
>       [ 0.53366791]])
>
>  
>
>>>y[idx,0]
>>>      
>>>
>matrix([[ 0.63731308,  0.34282663,  0.53366791]])
>
>I was expecting a column vector.
>
>  
>
This should be better behaved now in SVN.  Thanks for the reports.

-Travis

Re: [Numpy-discussion] indexing bug in numpy r2694

[Keith G. <kwg...@gm...>]

On 6/28/06, Travis Oliphant <oli...@ee...> wrote:
> Keith Goodman wrote:
>
> >On 6/28/06, Pau Gargallo <pau...@gm...> wrote:
> >
> >
> >>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)
> >>
> >>
> >
> >What about the second issue? Is this expected behavior?
> >
> >
> >
> >>>idx
> >>>
> >>>
> >array([0, 1, 2])
> >
> >
> >
> >>>y
> >>>
> >>>
> >
> >matrix([[ 0.63731308],
> >       [ 0.34282663],
> >       [ 0.53366791]])
> >
> >
> >
> >>>y[idx]
> >>>
> >>>
> >
> >matrix([[ 0.63731308],
> >       [ 0.34282663],
> >       [ 0.53366791]])
> >
> >
> >
> >>>y[idx,0]
> >>>
> >>>
> >matrix([[ 0.63731308,  0.34282663,  0.53366791]])
> >
> >I was expecting a column vector.
> >
> >
> >
> This should be better behaved now in SVN.  Thanks for the reports.

Now numpy can do

y[y > 0.5]

instead of

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

where, for example, y = asmatrix(rand(3,1)).

I know I'm pushing my luck here. But one more feature would make this perfect.

Currently y[y>0.5,:] returns the first column even if y has more than
one column. Returning all columns would make it perfect.

Example:

>> y

matrix([[ 0.38828902,  0.91649964],
       [ 0.41074001,  0.7105919 ],
       [ 0.15460833,  0.16746956]])

>> y[y[:,1]>0.5,:]

matrix([[ 0.38828902],
       [ 0.41074001]])

A better answer for matrix users would be:

>> y[(0,1),:]

matrix([[ 0.38828902,  0.91649964],
       [ 0.41074001,  0.7105919 ]])

Re: [Numpy-discussion] indexing bug in numpy r2694

[Keith G. <kwg...@gm...>]

On 6/28/06, Travis Oliphant <oli...@ee...> wrote:
> This should be better behaved now in SVN.  Thanks for the reports.

I'm impressed by how quickly features are added and bugs are fixed.
And by how quick it is to install a new version of numpy.

Thank you.