[Tutor] How to sum rows and columns of a matrix?

[Liam Clarke]

There's a specific package for arrays 

http://www.stsci.edu/resources/software_hardware/numarray

that implements array mathematics. I use it for pixel map manipulation
in pygame, so it's relatively fast.


On Mon, 31 Jan 2005 19:09:59 +0100, Gregor Lingl <glingl at aon.at> wrote:
> Hi all of you,
> 
> I'm representing a 4x4 matrix as a 16-element list, e.g.
> 
> m=range(16)
> 
> first 4 elements first row, second four elements second row etc.
> I want to sum rows and columns like
> 
> i-th row:
> 
> sum(m[4*i:4*i+4])
> 
> and ith column:
> 
> sum(m[i::4])
> 
> This seems to be slow because of the formation of the slices.
> I wonder if there is a way using generators or generator-expressions
> (which I didn't study yet) to compute these sums without copying
> parts of the matrix to a new list. (I'd guess that there should exist
> some canonical generator for sequences, which produces their elements
> ..., maybe also for slices ?)
> 
> All comments, hints, solutions are welcome.
> 
> Regards,
> Gregor
> 
> --
> Gregor Lingl
> Reisnerstrasse 3/19
> A-1030 Wien
> 
> Telefon: +43 1 713 33 98
> Mobil:   +43 664 140 35 27
> 
> Autor von "Python für Kids"
> Website: python4kids.net
> _______________________________________________
> Tutor maillist  -  Tutor at python.org
> http://mail.python.org/mailman/listinfo/tutor
> 


-- 
'There is only one basic human right, and that is to do as you damn well please.
And with it comes the only basic human duty, to take the consequences.