Difference between array( [1,0,1] ) and array( [ [1,0,1] ] )

[Stephen Tucker]

Markos,

I can explain the difference from a non-numpy point of view - I hope you
will be able to see how this difference affects what you are trying to do
in numpy.

vector_1 is an np.array consisting of a three-element list, with the three
elements being 1, 0 and 1.

vector_2 is an np.array consisting (at the top level) of a one-element
list, with that element (at this top level) being a three-element list,
with these three elements (at the lower level) being 1, 0 and 1.

Stephen.




On Fri, Jun 21, 2019 at 7:29 AM Markos <markos at c2o.pro.br> wrote:

>
> Hi,
>
> I'm studying Numpy and I don't understand the difference between
>
> >>> vector_1 = np.array( [ 1,0,1 ] )
>
> with 1 bracket and
>
> >>> vector_2 = np.array( [ [ 1,0,1 ] ] )
>
> with 2 brackets
>
> The shape of vector_1 is:
>
> >>> vector_1.shape
> (3,)
>
> But the shape of vector_2 is:
>
> >>> vector_2.shape
> (1, 3)
>
> The transpose on vector_1 don't work:
>
> >>> vector_1.T
> array([1, 0, 1])
>
> But the transpose method in vector_2 works fine:
>
> >>> vector_2.T
> array([[1],
>         [0],
>         [1]])
>
>
> I thought that both vectors would be treated as an matrix of 1 row and 3
> columns.
>
> Why this difference?
>
> Any tip?
>
> Thank you,
> Markos
> --
> https://mail.python.org/mailman/listinfo/python-list
>