[Numpy-discussion] block matrix and sums of blocks

Charles R Harris charlesr.harris@gmail....
Sun Feb 22 19:55:39 CST 2009


On Sun, Feb 22, 2009 at 6:39 PM, Xavier Gnata <xavier.gnata@gmail.com>wrote:

> Hi,
>
> Let us consider one kN x kM array.
> What is the fastest way to sum each k x k square block of A and to put
> all these results into a NxM array B?
>
> For instance:
> If A =
> [112233
>  112233
>  223311
>  223311]
> then B =
> [4 8 12
>  4 12 4]
>
> No sanity checks on the arrays shapes are requiered. Only speed matters ;)
>

An example with real numpy arrays would help ;) But basically you will need
to reshape the matrix and sum along the last axis.

Chuck
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