[Numpy-discussion] Specifying Index Programmatically
Neil Martinsen-Burrell
nmb@wartburg....
Sat Aug 8 22:54:35 CDT 2009
On 2009-08-08 22:46 , T J wrote:
> I have an array, and I need to index it like so:
>
> z[...,x,:]
>
> How can I write code which will index z, as above, when x is not known
> ahead of time. For that matter, the particular dimension I am querying
> is not known either. In case this is still confusing, I am looking
> for the NumPy way to do:
>
> z[("...",5,":")]
>
> z[(":", 3, ":", 5, "...")]
>
> z[(1, "...", 5)]
>
> Basically, I want to be able to pre-construct what should appear
> inside the []. The numbers are no problem, but I'm having trouble
> with the ellipsis and colon.
The ellipsis is a built-in python constant called Ellipsis. The colon
is a slice object, again a python built-in, called with None as an
argument. So, z[...,2,:] == z[Ellipsis,2,slice(None)].
-Neil
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