[Numpy-discussion] Can not update a submatrix

Charles R Harris charlesr.harris@gmail....
Wed Jan 30 09:27:34 CST 2008


On Jan 30, 2008 8:21 AM, Nadav Horesh <nadavh@visionsense.com> wrote:

>  But:
>
>
> >>> R[ax,:] = 100
> >>> R
> array([[  0,   1,   2],
>        [100, 100, 100],
>        [100, 100, 100]])
> >>> R[:,ax] = 200
> >>> R
> array([[  0, 200, 200],
>        [100, 200, 200],
>        [100, 200, 200]])
>
> Do I get an array view only if the array is contiguous?
>

You get an array view if the elements can be addressed with offsets,
strides, and counts. Think nested for loops.

In [1]: a = zeros((4,4))

In [2]: a[::2,::2] = 1

In [3]: a
Out[3]:
array([[ 1.,  0.,  1.,  0.],
       [ 0.,  0.,  0.,  0.],
       [ 1.,  0.,  1.,  0.],
       [ 0.,  0.,  0.,  0.]])

Chuck
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