# [Numpy-discussion] matrix indexing question

Paulo Jose da Silva e Silva pjssilva@ime.usp...
Sun Mar 25 12:48:44 CDT 2007

```Em Dom, 2007-03-25 às 13:07 -0400, Alan G Isaac escreveu:

> So this ::
>
>     >>> x[1]
>     matrix([[1, 0]])
>
> feels wrong.  (Similarly when iterating across rows.)
> Of course I realize that I can just ::
>
>     >>> x.A[1]
>     array([1, 0])
>
> but since the above keeps feeling wrong I felt I should
> raise this as a possible design issue, better discussed
> early than latter.

I think the point here is that if you are using matrices, then all you
"should" want are matrices, just like in MATLAB:

>> A = [1 2; 3 4]

A =

1     2
3     4

>> b = A(1, :)

b =

1     2

>> size(b)

ans =

1     2

>> b = A(:, 1)

b =

1
3

>> size(b)

ans =

2     1

>> b = 1

b =

1

>> size(b)

ans =

1     1

You see, rows, columnes, and even numbers, are treated as matrices.

Paulo

--
Paulo José da Silva e Silva
Professor Assistente do Dep. de Ciência da Computação
(Assistant Professor of the Computer Science Dept.)
Universidade de São Paulo - Brazil

e-mail: rsilva@ime.usp.br           Web: http://www.ime.usp.br/~rsilva

Teoria é o que não entendemos o     (Theory is something we don't)
suficiente para chamar de prática.  (understand well enough to call practice)

```