[SciPy-user] In-place matrix reordering

Antonino Ingargiola tritemio@gmail....
Wed Feb 25 04:31:25 CST 2009

2009/2/25 Robert Kern <robert.kern@gmail.com>:
> On Wed, Feb 25, 2009 at 02:12, Antonino Ingargiola <tritemio@gmail.com> wrote:
>> Hi to the list,
>> I have to "reorder" the columns of a big 2D array (a matrix) but
>> without doing a temp copy of the whole matrix (since it is 1.5GB).
>> Basically I would need something like this:
>> a = arange(12).reshape(4,3)
>> b = a[:,(2,0,1)]
>> but without the array copy triggered by the advanced indexing. Let the
>> (2,0,1) tuple be an arbitrary sequence previously computed.
>> The .take method seems to do a copy too:
>> b = a.take((2,0,1), axis=1)
>> What I need is a "view" of "a" with an arbitrary column order.
>> Is there a way to accomplish this task?
> No, sorry. numpy's memory model does not allow arbitrary views like this.

Is there any workarounds to save ram in this case? Something like
using an external package or inline C (I have no idea about that).


   ~ Antonio

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