[Numpy-discussion] matrix indexing question

Colin J. Williams cjw@sympatico...
Sun Mar 25 18:20:21 CDT 2007


Alan G Isaac wrote:
>> Em Dom, 2007-03-25 Ã s 13:07 -0400, Alan G Isaac escreveu:
>>>     >>> x[1]
>>>     matrix([[1, 0]])
>>> feels wrong.  (Similarly when iterating across rows.)
> 
> 
> On Sun, 25 Mar 2007, Paulo Jose da Silva e Silva apparently wrote:
>> I think the point here is that if you are using matrices, 
>> then all you "should" want are matrices, just like in 
>> MATLAB:
>>         >> b = A(1, :)
>>         b =
>>              1     2
> 
> 
> Yes, that is the idea behind this, which I am also 
> accustomed to from GAUSS.  But note again that the Matlab 
> equivalent ::
> 
>     >>> x=N.mat('1 2;3 4')
>     >>> x[0,:]
>     matrix([[1, 2]])
> 
> does provide this behavior.  The question I am raising
> is a design question and is I think really not addressed
> by the rule of thumb you offer.  Specifically, that rule
> of thumb if it is indeed the justification of  ::
> 
>     >>> x[1]
>     matrix([[3, 4]])
> 
> finds itself in basic conflict with the idea that I ought to 
> be able to iterate over the objects in an iterable container.
> 
> I mean really, does this not "feel" wrong? ::
> 
>     >>> for item in x: print item.__repr__()
>     ...
>     matrix([[1, 2]])
>     matrix([[3, 4]])
> 
> Cheers,
> Alan Isaac
> 
> 
Perhaps this would be clearer with:

    >>> for rowVector in x: print item.__repr__()
     ...
     matrix([[1, 2]])
     matrix([[3, 4]])

Colin W.




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