[Numpy-discussion] yet another indexing question

Chris.Barker Chris.Barker@noaa....
Mon Oct 17 12:13:32 CDT 2011


On 10/14/11 5:04 AM, Neal Becker wrote:
> suppose I have:
>
> In [10]: u
> Out[10]:
> array([[0, 1, 2, 3, 4],
>         [5, 6, 7, 8, 9]])
>
> And I have a vector v:
>   v = np.array ((0,1,0,1,0))
>
> I want to form an output vector which selects items from u where v is the index
> of the row of u to be selected.

> Now, more importantly, I need the result to be a reference to the original array
> (not a copy), because I'm going to use it on the LHS of an assignment.  Is this
> possible?

No, it's not. numpy arrays need to be describable with regular strides 
-- when selecting arbitrary elements from an array, there is no way to 
describe the resulting array as regular strides into the same data block 
as the original.

-Chris



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Christopher Barker, Ph.D.
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