Liam Clarke wrote:
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.
Here is one way to do what you want using numarray:
>>> import numarray
Create a 4x4 array:
>>> m=numarray.array(range(16),shape=(4,4))
>>> m
array([[ 0, 1, 2, 3],
[ 4, 5, 6, 7],
[ 8, 9, 10, 11],
[12, 13, 14, 15]])
Row access:
>>> m[1]
array([4, 5, 6, 7])
Column access:
>>> m[:,1]
array([ 1, 5, 9, 13])
Sum all the rows:
>>> [sum(m[i]) for i in range(4)]
[6, 22, 38, 54]
Sum all the columns:
>>> [sum(m[:,i]) for i in range(4)]
[24, 28, 32, 36]
Kent
On Mon, 31 Jan 2005 19:09:59 +0100, Gregor Lingl <[EMAIL PROTECTED]> 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
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