[Numpy-discussion] shape, size

Todd Miller jmiller at stsci.edu
Fri Jan 30 13:50:02 CST 2004


On Thu, 2004-01-29 at 23:12, Daniel Holth wrote:
> In python, if na is a numarray:
> 
> >>> na
> array([[0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0],
>        [1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1]])
> 
> I can type
> 
> >>> nb = na[:,:4]
> >>> nb
> array([[0, 1, 0, 1],
>        [1, 0, 1, 0]])
> 
> >>> nb[0][0]=17
> 
> >>> na
> array([[17,  1,  0,  1,  0,  1,  0,  1,  0,  1,  0,  1,  0,  1,  0],
>        [ 1,  0,  1,  0,  1,  0,  1,  0,  1,  0,  1,  0,  1,  0,  1]])
> 
> nb and na share data.
> 
> How do you write nb = na[:,:4] in a C extension module?

Here's the quick and dirty way:

nb = (PyArrayObject *) PyObject_CallMethod(na, "view", NULL);
if (na->dimensions[1] >= 4)
	nb->dimensions[1] = 4;

Todd
> 
> Thanks,
> 
> Daniel Holth
> 
> 
> 
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Todd Miller 			
Space Telescope Science Institute
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