[Numpy-discussion] Array views
srean
srean.list at gmail.com
Sat Mar 26 13:32:24 EDT 2011
Hi,
I am also interested in this. In my application there is a large 2d array,
lets call it 'b' to keep the notation consistent in the thread. b's
columns need to be recomputed often. Ideally this re-computation happens in
a function. Lets call that function updater(b, col_index): The simplest
example is where
updater(b, col_index) is a matrix vector multiply, where the matrix or the
vector changes.
Is there anyway apart from using ufuncs that I can make updater() write the
result directly in b and not create a new temporary column that is then
copied into b ? Say for the matrix vector multiply example.
I can write the matrix vector product in terms of ufuncs but will lose out
in terms of speed.
In the best case scenario I would like to maintain 'b' in a csr sparse
matrix form, as 'b' participates in a matrix vector multiply. I think csr
would be asking for too much, but even ccs should help. I dont want to
clutter this thread with the sparsity issues though, any solution to the
original question or pointers to solutions would be appreciated.
Thanks
--srean
On Sat, Mar 26, 2011 at 12:10 PM, Hugo Gagnon <
sourceforge.numpy at user.fastmail.fm> wrote:
> Hello,
>
> Say I have a few 1d arrays and one 2d array which columns I want to be
> the 1d arrays.
> I also want all the a's arrays to share the *same data* with the b
> array.
> If I call my 1d arrays a1, a2, etc. and my 2d array b, then
>
> b[:,0] = a1[:]
> b[:,1] = a2[:]
> ...
>
> won't work because apparently copying occurs.
> I tried it the other way around i.e.
>
> a1 = b[:,0]
> a2 = b[:,1]
> ...
>
> and it works but that doesn't help me for my problem.
> Is there a way to reformulate the first code snippet above but with
> shallow copying?
>
> Thanks,
> --
> Hugo Gagnon
> --
> Hugo Gagnon
>
> _______________________________________________
> NumPy-Discussion mailing list
> NumPy-Discussion at scipy.org
> http://mail.scipy.org/mailman/listinfo/numpy-discussion
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/numpy-discussion/attachments/20110326/bbe27581/attachment.html>
More information about the NumPy-Discussion
mailing list