[Numpy-discussion] dimension aligment

Thomas Hrabe thrabe@burnham....
Tue May 20 12:58:08 CDT 2008


I am wandering what shape would be like in C

would it be 
{4;2;3} or
{3;2;4} 

?

so 
shape[0] == 4 
or
shape[0] == 3



-----Original Message-----
From: numpy-discussion-bounces@scipy.org on behalf of Charles R Harris
Sent: Tue 5/20/2008 10:56 AM
To: Discussion of Numerical Python
Subject: Re: [Numpy-discussion] dimension aligment
 
On Tue, May 20, 2008 at 11:47 AM, Thomas Hrabe <thrabe@burnham.org> wrote:

>
> Hi all,
>
> just a simple question regarding the alignment of dimensions:
>
>
> given a 3d array
> a =
> numpy.array([[[1,2,3],[4,5,6]],[[7,8,9],[10,11,12]],[[13,14,15],[16,17,18]],[[19,20,21],[22,23,24]]])
> a.shape
> returns (4,2,3)
>
> so I assume the first digit is the 3rd dimension, second is 2nd dim and
> third is the first.
>

Only if you count from the right. I would call the first digit the first
dimension.

>
> how is the data aligned in memory now?
> according to the strides it should be
> 1,2,3,4,5,6,7,8,9,10,...
> right?
>
Like a C array, contiguous and the rightmost dimension varies fastest.

>
> if I had an array of more dimensions, the first digit returned by shape
> should always be the highest dim.
>
Yes. Athough first is less ambiguous than highest

Chuck

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